Development of the Aril Irises (under construction)
by John J. Taylor and Thomas M. Wilkes from Chapter 11, Arils and Arilbreds in "The World of Irises" © 1978 AIS
THE ARIL IRISES
The aril species listed and classified in Chapter 1 will be grouped and described here as the oncocycli, the regelias, the falcifolias (technically, hexapogons), the psammirises (including the arenaria-flavissima complex) and the pseudoregelias (Taylor 1976).
The common characteristic of these groups is the aril, a creamy white appendage at one end of their seeds. The aril is especially conspicuous in the oncocycli in which it is sometimes as large as the balance of the seed. It is also relatively large in the regelias, but in the other aril groups is much smaller than the seeds.
The terminology for the aril hybrids has been confusing. Members of the Aril Society International
have attempted to resolve the matter by developing standard horticultural definitions.
By these definitions, the name "aril" (first used in this sense by the late Lloyd Austin
) refers to all species with arillate seeds, and to hybrids derived solely from two or more such species.
The term "onco" applies solely to the oncocyclus species and to hybrids involving onco species only. Similarly, the term "regelia" is limited to regelia species and their hybrids. A first or advanced generation hybrid between regelia and oncocyclus species or hybrids is known as a "regeliocyclus" (plural, "regeliocycli").
The word "arilbred" refers to hybrids from crosses of the aril species or hybrids with tall bearded and other eupogon irises. This is a broad term which encompasses the "oncobreds" from crosses between oncos or onco hybrids and the bearded irises, e.g., 'William Mohr'
and other "Mohr" irises; the "regeliabreds" from crosses between regelias and bearded irises, e.g., 'Saffron Charm'
and 'Hoogpum Blue'
; arilbreds which have onco, regelia and bearded irises in their ancestries, e.g., 'Ardrun'
, 'Tiny Tyke'
and the well-known C. G. White arilbreds; and the arilbred dwarfs derived from the psammirises, e.g., 'Promise'
THE ONCOCYCLUS IRISES
More than 50 onco species, some with several varieties, have been recorded in the literature. Many of the species described are undoubtedly local varieties of other species, some are identical with others, and several apparently are hybrids (Bastow 1968; Furse 1971; Rodionenko 1968, 1972). Until detailed studies of the oncos are made it seems best to retain their historic names, though many of them may ultimately be reduced to varietal names or be listed as synonyms.
The oncos occur in Israel, Jordan, Syria, Lebanon, Turkey, Iran, Iraq, and in the Russian Caucasus well into Georgia. The more northern oncos are hardy mountain and steppe plants. Those in Syria and Lebanon are usually found on the eastern slopes of the high mountains bordering the Mediterranean and in the more arid areas east of those mountains. Few oncos are truly desert irises except for occasional species found in the Negev Desert and in some semidesert areas of Syria.
Oncocyclus colonies may be small and isolated, or they may be scattered along mountain ranges for several hundred miles. Two or more species are sometimes found growing together. In the Russian Caucasus there is evidence of hybridization between such sympatric species. These hybrids have been studied in some detail, and some have been experimentally reproduced (Rodionenko 1968). Hybrid swarms have also been reported in Turkey and Iran (Furse 1968, 1971).
Extensive variation exists within the onco group, not only from one species to another, but also among individual clones of a particular species. Some characteristics, however, are common to many. All oncos bloom on single-flowered stems, sometimes so short that the species are true dwarfs. Most oncos have red-skinned rhizomes which multiply from nipple-shaped increases; a few are stoloniferous. Usually oncos have well-defined signal patches and broad diffuse beards on the falls. Many species are patterned, the standards less conspicuously marked than the falls, but a few are essentially selfs. Patterns vary from intense speckling and stippling to exquisitely fine veining and dotting. The standards produce a globular or occasionally a conical form, and frequently appear to be considerably larger than the falls, an effect sometimes created by the recurving falls. Styles are large and often protrude beyond the standards.
The falls of most species are rounded, but may be pointed or strap shaped. Although the standards are usually delicately marked, the falls are often quite heavily patterned, sometimes with the markings almost completely covering the ground color. Normally the falls are recurved, occasionally sharply so, but they may be flaring. The signals are generally large and contrastingly colored, although a few species lack defined signals.
(figure 1) is perhaps the best known and most widely grown onco species. It has been cultivated in Europe since 1573 when, according to Dykes, it was imported from Constantinople. Its large globular blooms present a spectacular if somber appearance, hence the popular name "Mourning Iris." The large, closed and domed standards are lighter than the falls, with the creamy white ground covered with dark brownish purple veins, stipples and dots. The broad, rounded and recurved falls are even more heavily patterned with coarse broken veins and speckles almost obscuring the light creamy ground. The styles are prominent, and the crests are distinctly marked. The falls have large black-purple signals and diffuse brownish black beards. Although the original habitat of I. susiana is unknown, some suspect that it may have been in Syria or Lebanon where related large-flowered, spotted oncos allied to I. sofarana
now occur (Kenneth Bastow
1968, Carolyne Weymouth and Saukat Chaudhary
, native to Turkey, is the giant of the oncos; some specimens have flowers 20 cm (8 inches) in diameter. It is almost a self, usually gray and often with a greenish or greenish yellow cast. Standards are tall, closed, orbicular, reflexed outward from the midrib, and veined inconspicuously in pale violet. The falls are broad, rounded, recurved and lightly veined violet. The signals are small or missing; the beards are a light mustard color. At a distance of one or two meters the· pale markings are not apparent and the flower appears as a large, silvery gray, globular bloom with dominant standards.
The disproportion between the standards and falls common to many of the oncos reaches its extreme in I. paradoxa
. Its thick, flaring, abbreviated, strap-shaped falls are about 4-5 cm (1.5-2 inches) long and only 12-18 mm (0.5-0.8 inch) wide. It is certainly the most unusual of the oncos, perhaps not beautiful, but grotesquely fascinating. The standards are erect, orbicular, widening out from a short narrow claw, and usually four or five times as wide as the falls. In most forms standards are some shade of violet purple, from pale to quite dark, with even darker veins. The styles are short, dark, and have small crests. The falls have contrasting chevron bands near their tips, and thick velvety black-purple beards. This native of Russia and Iran blooms on short 8-15 cm (3-6 inch) stems, but the diameter at the standards is 7.5 cm (3 inches) or more.
Typical I. acutiloba
, also a native of Russia and Iran, is apparently rare in cultivation. Most of the clones so labeled at present are the variety lineolata Trautv., a closely related form with much narrower petals. All members of the I. acutiloba group have flowers with elongated, narrowly lanceolate, pointed petals. I. acutiloba, a variable small species with 5-8 cm (2-3 inch) stems has relatively tall, conical standards 5-8 cm (2-3 inches) long and 12-20 mm (0.5-0.8 inches) wide, and almost horizontal falls about the same size as the standards. The ground color of all petals is ivory white to pale violet, veined deeper. Some specimens have a pinkish cast. The signal patch is fairly large, almost round, and usually bright maroon red. Styles are relatively short.
, from Turkey and the Caucasus, and the closely related I. elegantissima
are noted for their rather broad, ovoid, spoon-shaped falls, and for their long, pendent styles which conform tightly to the contour of the falls. The broad standards are usually silvery white or gray veined in light purple violet, and are generally closed at the tips to look almost spherical. The falls are heavily marked with dense veining and stippling, almost totally obscuring the light cream to yellow ground color. The intensely dark, plushy signals are triangular and partly covered by the styles. The beards of short, purple-brown hairs are diffuse. Stems vary from 2.5-25 cm (1-10 inches). Variations in size, form and color of flowers are common in this species.
is perhaps the most beautiful of the oncos and bears its large flowers on sturdy stems about 30 cm (1 foot) tall. The erect, domed, closed and slightly ruffled standards vary from white to pale pinkish violet, and are veined inconspicuously in pale violet. The gradually recurved, broad, rounded falls have a creamy ground color covered with minute crimson dots, sparse at the margins but dense in the central portions. The styles are prominent with crimson dots. Beards are of scattered light brown hairs. This species is a native of Syria and Israel. I. samariae
is similar but has flowers that are pinker and more ruffled (figure 1).
The well-known I. barnumae
and I. helenae
(syn. I. mariae
) are thought to be related to I. polakii
, a somewhat obscure species. The medium-sized flowers of these species are borne on relatively short stems, and are usually near selfs in dark shades of red purple or brownish purple approaching brown mahogany, veined darker. Falls are usually sharply recurved and have plushy black signals and beards of yellow hairs tipped purple. The standards are dominant, however, and are tall, orbicular and often closed.
These few examples must serve to illustrate the remarkable variation among the onco species and their innumerable forms and natural hybrids.
THE REGELIA IRISES
The regelia species are essentially montane plants inhabiting sunny mountain slopes, valleys and wet meadows from the vicinity of Tashkent in south-central USSR, east into the Tien Shan and Parnir-Alai regions, and south to the mountains of the Hindu Kush in Afghanistan. Although a few species have relatively restricted ranges, most are widely distributed. Occasionally two or more regelia species have been found in the same locality (Furse 1965, 1971; Grey-Wilson 1973; Rodionenko 1968), but natural hybrids have not been reported.
The regelias are characterized by fleshy to wiry rhizomes that are often red skinned and more or less stoloniferous. Each stem bears one to three flowers, usually with all petals bearded, although beards on standards may be irregular or lacking in some forms. Most species are patterned with overall veining sometimes complemented by a contrasting edging, though selfs and near selfs also occur. Falls are generally darker than standards. In some diploid species, coarse veins may coalesce near the ends of the beards to produce dark, often roughly triangular signal areas.
is probably the best known and most commonly grown of the regelias. The tall, broadly conical standards have given it the name "Pagoda Iris." Two (rarely three) flowers are borne on stems 25-60 cm (10-23 inches) tall. All petals have about the same ground color which varies from a grayish white to cream and the palest tints of yellow green and dull olive gray. Several conspicuous veins of greenish or purplish brown, chocolate or brown black lie nearly parallel to the midribs, while thinner less obtrusive veins obliquely mark the rest of the blades. The bases of the standards are often stained green to brown, and bearded on the inner surface with a few to many violet-brown to almost black hairs. The falls have similar, usually thicker beards which end at triangular signal blotches of the same dark color as the veins. Styles are reddish brown to brown, and conceal stamens with purplish filaments and anthers with bluish pollen. The collected variety concolor has the same form as the type, but is a uniform blue violet with faint concolorous venation. Since the end of the last century, several forms of I. korolkowii have been selected from cultivated seedlings and collections, and introduced as 'Atropurpurea'
, 'Brown and Green'
. Some of these are no longer in cultivation, some are probably hybrids, and some are not distinctive. Recently a clone resembling Foster's 'Leichtliniana' was discovered in Afghanistan (Furse 1968).
is similar to I. korolkowii. Its 20-37 cm (8-15 inch) stems bear two or three flowers with rather narrow pointed light greenish yellow petals conspicuously patterned with raspberry to brown-purple veins. Bluish beards extend onto the blades of the falls and end at prominent dark signal blotches. In some specimens standards may be only weakly or not at all bearded.
somewhat resembles I. darwasica except that its clear yellow standards lack contrasting venation, and bear thick greenish yellow beards quite unlike the purple to purple-black beards on the falls. This attractive species is readily though not widely cultivated.
is a bizarre species with violet to violet-brown petals less than 15 mm (0.6 inch) wide, and falls without conspicuous signals. Flowering on 60-70 cm (24-28 inch) stems,
is the tallest of the regelia species. The flowers are light lavender-blue, purple-violet or bluish violet selfs. The petals have a silky texture and iridescence not found in other bearded irises. A few scattered orange hairs beard the standards, while dense beards of bright gold to orange hairs tipped cinnamon extend out onto the blades of the falls. A form with semi-flaring falls, and several named color selections including 'Blue Joy
and 'Late Amethyst'
have been introduced. Perhaps the most unusual is the form 'Alba'
that opens a light grayed blue then fades to cool white in warm climates, but remains an icy blue self in cool weather. The infertility of the form 'Purpurea'
as well as its mauve-violet petals and bronze-blue beards suggest that it is a hybrid of I. hoogiana, perhaps with 'Korolkowii Concolor'
is also a blue-purple to blue-violet self with lighter styles and pale purple or lavender beards. It produces one or two dainty flowers on stems only 5-20 cm (2-8 inches) high (Grey-Wilson 1973).
(figure 1), a Russian species, produces two or three gaily colored, lightly ruffled flowers on each 30-60 cm (12-24 inch) stem. The petals are usually pale lilac to reddish purple blending to bright blue or violet blu·e near the limbs, and veined and bordered bronze, reddish brown or brown. Bluish to yellowish beards are conspicuous on both standards and falls. There is considerable clonal variation in both intensity and dispersion of beard and petal pigmentation in I. stolonifera. Nearly a dozen color selections have been introduced under botanical or cultivar names, including I. leichtlini
, I. vaga
, I. vaga compacta
, 'Decorated Blue Beard'
, 'Decorated Delight'
, 'Decorated Giant'
, 'Real Harmony'
, 'Red White and Blue'
, and 'Zwanenburg Beauty'
. The form 'Conical', a rosy mulberry self, is probably a hybrid with 'Korolkowii Concolor'
is a recently described species. The sharply recurved falls are pale cream veined purple red and stained bronze near the tips. Standards are erect and flushed darker than the falls. Styles are pale purple and beards lavender (Grey-Wilson 1973).
THE PSAMMIRISES-I. HUMILIS, I. BLOUDOWII
Psammirises I. humilis
is the correct term for the irises popularly known as "arenaria-flavissima" See note in chapter 1.] are found in sandy or gritty soils of open meadows and hillsides from Hungary and Austria east into Transcaucasian USSR, and on exposed mountain slopes and in grasslands and shaded dry mountain valleys from central Siberia north and east into Mongolia, Manchuria and Transbaikalian USSR. They are the most widely distributed of the aril species, and are the only arils native to central Europe.
Although there are some differences in stem length and rhizome morphology among psammirises, all are characterized by stems less than 25 cm (10 inches) bearing one to three bright yellow flowers with flaring falls often marked with brownish purple veins. The flowers are short-lived, and in the common forms, twist into tight corkscrews when withering. Several species are popular among dwarf iris fanciers.
THE PSEUDOREGELIA IRISES
The pseudoregelias occur from the Indian Himalayas north and east into Nepal, Tibet, Mongolia and eastern Siberia, and west into west-central Siberia. They are all essentially montane or alpine species found at elevations of up to 5500 m (18,000 feet).
The pseudoregelia species are remarkably similar in appearance. Stems are very short or missing in I. kamaonensis
and in the other species they rarely exceed 15 cm (6 inches), usually bearing one to two bluish mauve to purple flowers mottled with darker violet to blue-violet spots. White forms, sometimes with pale blue-gray markings, have been observed by Dykes (1916), and by Synge from Nepal in 1975. Synge also reported an occurrence there of I. goniocarpa
. None of the flowers are long lasting. I. hookeriana
, I. kamaonensis
and I. tigridia
are the most frequently seen in American gardens.
THE FALCIFOLIA IRISES
The falcifolias are xerophytic natives of the Turkmenian and Uzbekian deserts of south-central USSR, and of a few similar but restricted localities in Iran and Afghanistan. 2 The two known species, I. falcifolia
and I. longiscapa
, have weakly stoloniferous or nonstoloniferous rhizomes, very narrow grasslike leaves, and thin, leafless stems up to 100 cm (40 inches) tall. Two to five small greenish mauve, lilac or violet flowers are produced on each stem. All petals are narrow, the startdards even strap-shaped. Beards are yellow or yellowish gray, and may be sparse or missing from the standards. 3 Falcifolias are rare in cultivation.
HYBRIDIZATION OF ARILS
Although oncos do not set seed well when self-pollinated, the many species are all interfertile as are most different seed-grown clones of any one of the species. Both their chromosome similarities (L. Fitz Randolph
and J. Mitra
1960, Carolyne Weymouth and Shaukat Chaudhary
1974), and the fertility of hybrids between them indicate that onco species are closely related.
Because of their interfertility, it is probable that most conceivable crosses have been made between the common onco species. However, since the end of the nineteenth century when Foster produced a number of onco hybrids, few have been registered and introduced into commerce. Most have been distributed as relatively easily grown pedigreed seedlings from involved breeding with several onco species.
Diploid, triploid and tetraploid regelia hybrids have been produced, and a number have been distributed. Most available commercially are attractive triploids derived from crosses between diploid forms of I. korolkowii
and the tetraploid species, I. hoogiana
and I. stolonifera
. Though these triploids are usually infertile, some will occasionally set a few seeds.
In contrast, 'Vera'
(figure 3), probably also from diploid x tetraploid breeding, is a fertile tetraploid which resulted apparently from an unreduced garnete .. 4 Vera and the tetraploid 'Bronze Beauty'
X I. stolonifera
) have been intercrossed and backcrossed and outcrossed to diploid, triploid and tetraploid regelia species and hybrids. Many such advanced generation hybrids are variably and exceptionally colorful, often having the silky texture of I. hoogiana, and the petal pigment patterns of I. stolonifera. Most are fertile, vigorous, and decidedly worth developing for cool climates. New colors, patterns, and other floral and growth characteristics may be expected in regelia hybrids when the newer species are more widely grown (figure 2)
ENDNOTES 2. Per Wendelbo
and Brian Mathew
(1975) wrote that Iris falcifolia has a general distribution through the "Regelia belt," NE Persia, Afghanistan, West Pakistan, the Kizyl Kum and Kara Kum, on more or less sandy plains. 3. The unique characteristics of I. /ongiscapa are documented by a photograph of a herbarium specimen (Lawrence 1%1) with the description, " ... the peculiar and distinctive features are in the inflorescence and the flowers. Each main stem bears from three to five flowers that are nearly two inches across, and each flower stands on a slender wiry pedicel some two to three inches beyond the spathe valves. The pair of spathe valves themselves are borne on a short peduncle that varies from one half to one inch in length:' 4. The author's statements are based upon his crosses with Vera including Vera X Bronze Beauty, I. hoogiana x Vera, and Bronze Beauty x I. hoogiana. His count of Vera, 2n = 42-45.
Intersectional hybrids between regelias and oncos are the well-known regeliocycli. The cross has been made both ways, but more seeds with higher germination rates have been obtained with diploid regelias as pollen parents. Agatha was the first of many regeliocycli introduced by the Van Tubergen firm in 1895 and, still grows in some historical collections. This and other Van Tubergen varieties may be recognized by their mythological names, attractive flowers like those of regelias or oncos on two-flowered stems, and vigor and ease of cultivation.
Regeliocycli have been useful in aril breeding. Diploid varieties are fertile when intercrossed, and partly fertile in backcrosses and outcrosses to diploid regelia or onco species or hybrids. Progeny from such crosses are generally more fertile than the parent regeliocycli, and both seed sets and germination rates are improved, especially when the regeliocyclus is the pollen parent.
Many clones from onco x regeliocyclus breeding were selected for oncolike appearance and introduced by Lloyd Austin
, Herbert Kerr
and Leo Clark
. Most have large, globular blooms on plants somewhat more easily grown than their onco parents. Although only a few of their clones have been registered, C. G. White
, Kerr, Clark, Frank Bushey
and John Holden
also produced a prodigious number of advanced generation hybrids of the general type onco x (onco x regeliocyclus). Those distributed exhibit few regelia traits. All are about as pod-fertile as onco species, but some produce no pollen. Though there has been much less interest in intercrossing regeliocycli, and in crossing regeliocycli with regelias, offspring from such crosses are usually extremely vigorous and may be selected for floral characteristics varying from nearly regelia to nearly onco. Some of them, e.g., Wilkes's
tetraploid from 'Persian Pansy'
x I. korolkowii 'Brown and Green'
, are worthy of introduction.
4. OTHER ARIL HYBRIDS
Few hybrids involving the remaining groups of arils have been reported. The psammiris hybrids which Paul Cook
produced by crossing I. bloudowii
and I. humilis
(flavissima) were only marginally fertile and apparently not distinctive. Much more numerous are the hybrids between psammirises and other aril species, including oncos, regelias and pseudoregelias. Kalich's hybrid between I. humilis
(arenaria) and I. hookeriana
was described as a lightly veined pink blend, while Emma Hobbs's Koviar
( I. korolkowii Violacea
x I. arenaria
) is a minuscule yellow-ground version of its pod parent, and an altogether delightful introduction. However, few such psammiris and pseudoregelia hybrids have survived beyond the seedling stage, and few have been described in bloom or distributed. It is likely that none are fertile.
BREEDING TETRAPLOID ARILS
Experience with irises as well as with many other kinds of plants indicates that tetraploid varieties are often more vigorous and usually produce more and larger flowers than their diploid counterparts. They may also be used to create fertile amphidiploid-like clones when crossed with other tetraploid species and cultivars. Unfortunately, with the exception of a few regelias, all the aril species are diploid.
Tetraploidy can be achieved by the use of colchicine (Appendix B) or by crossing diploids with tetraploids. The use of colchicine has not been productive with arils, and few successful efforts have been reported. More tetraploids are likely to result from diploid x tetraploid breeding. Evidence indicates that in diploids an unreduced gamete may occur once in a few hundred gametes. Such was the case with Van Tubergen's 'Vera'
( I. korolkowii
x I. stolonifera
). 'Sheik Jamil'
introduced by Tearington in 1975 from I. stolonifera
x 'Persian Pansy'
, is probably tetraploid. However, most offspring from diploid x tetraploid crosses will be triploid. Fortunately many triploid regeliocycli have some fertility, and these may be used fo develop tetraploids. When triploid regeliocycli are crossed with tetraploid regelias or regeliocycli, fertile tetraploids, as well as partly fertile triploids and aneuploids (those with one.or a few chromosomes more or less than balanced triploids and tetraploids) may be found among the progeny. From intensive intercrossing and backcrossing of such fertile hybrids, substantial families of tetraploid regeliocycli may be created.
CULTIVATION OF ARILS AND ARIL HYBRIDS
Except for some species growing on high mountain slopes, oncos are native to regions without summer rainfall. Soon after blooming their foliage dies and they remain dormant until autumn. During dormancy heat and moisture readily cause rot in the matured rhizomes, thus destroying the increase from which new plants develop.
During active growth in excellently drained beds, oncos tolerate considerable moisture. Where annual rainfalls exceed about 75 cm (30 inches) it is necessary to limit the water reaching the rhizomes, either by covering them or by digging them. Rhizomes, dug after the foliage dies, are washed and the dead leaves cut away. Cleaned and trimmed rhizomes are soaked in a compatible mixture of fungicide, insecticide and disinfectant, checked for EPA approval for irises. Rhizomes are then dried in the shade, and stored in dry sand or vermiculite in a warm dry place until fall planting time. Species that do not require annual division may be potted and the entire pot lifted and stored until autumn. Where adequate protection from winter damage cannot be assured, pots may be stored dry in a cool basement or refrigerator until spring.
Dormant rhizomes may also be protected without digging with covered A-frames, lean-tos, greenhouses, porch overhangs, cold frames, or similar covers which shed summer rains yet permit adequate ventilation. Such covered beds should also be protected from capillary water intrusion from the subsoil by a vapor barrier at the bottom of the bed. Vapor barriers are constructed when the beds are built by sloping the underlying soil layers a few decimeters so that water can drain out of the beds. Before the beds are filled, a 6-to 10-mil plastic sheet is installed along the back (upper level) and over the bottom of the bed. The bed is then filled with the plastic in place. This barrier assures that surface and soil water will not run into the beds, that capillary water will not intrude from below, and that any water falling on the bed will drain away.
Oncos are usually grown in a sunny location in beds built on natural slopes, or elevated 10-30 cm (4-12 inches) above the surrounding soil surface. To provide sharp drainage in the beds, each is dug 45-60 cm (18-24 inches) deep and layered at the bottom with 15 cm (6 inches) or more of crushed rock and coarse gravel. The beds are then filled with a mixture of coarse (washed builder's) sand and garden loam. Many successful growers dig into the upper 10-20 cm (4-8 inches) of soil 50-100 g (2-4 ounce) agricultural slaked lime per square meter (yard) and water it in well several weeks before planting, or 100-200 g (1/ 4-1/2 pound) pulverized dolomitic limestone or gypsum per square meter at the time of planting. Coarsely ground bone as well as a complete fertilizer such as 6-10-10 may also be incorporated. Humus, leafmold and similar organic materials may be added according to experience with your soil and climatic conditions.
Planting time is important in growing oncos. Roots must be well established, yet excessive foliage must not develop before hard frosts and cold winds occur. Oncos from warmer regions, such as I. mariae
, I. atrofusca
(figure 3), I. nazarena
, I. haynei
(figure 3), I. atropurpurea
and I. susiana
, tend to develop rapidly after planting, and should be planted several weeks after the slower growing and hardier mountain types like I. gatesii
, I. iberica
, I. sari
, I. paradoxa
, I. acutiloba
and I. urmiensis
(figure 3). In northern states planting should be completed by mid-September; in warmer areas, late October planting is recommended. When proper planting time of hybrids Of less well-known species is in doubt, it is better to plant with the warm-climate oncos. If top growth occurs in late autumn, a tilted cover to intercept and shed winter precipitation, and, if necessary, a loose mulch of excelsior or evergreen boughs when the ground freezes, will allow survival of many oncos even in severe climates.
b. REGELIAS AND REGELIOCYCLI
Although they may be cultivated like oncos, most regelias are generally less demanding and grow well in many open, sunny, well-drained nearly neutral soils. Dormant regelias should be protected from excess moisture in regions of high rainfall, or where soils are heavy or inadequately drained. Because regelias frequently begin top growth in late autumn, a light mulch and loose cover are recommended for winter protection.
In general, regeliocycli are cultivated as readily as regelias. Advanced generation hybrids obtained from backcrosses of older varieties to onco species or onco hybrids are more demanding and often must be grown like the oncos. Some of the psammirises have been grown as bright but fugitive rock garden and low border subjects for years. They are usually less fastidious than other aril species. Sandy or even stony soils containing a little loam or leaf mold, and partly or fully exposed to the sun, generally are suitable. Common psammirises grow actively throughout the summer and into autumn. They are perfectly winter hardy and tolerate moisture rather well, though soggy soils may prove lethal.
Pseudoregelias may be grown like regelias or oncos, though many gardeners have found them somewhat more difficult and less persistent. They begin active growth in early spring, flower while the leaves are still short, and require abundant water during the entire growing season. When the leaves begin to fade, water should be withheld, and the rhizomes protected from moisture until growth begins again the following spring. Some successful growers dig, clean and pot dormant rhizomes in gritty soil, then store the pots in an alpine house, cool basement or refrigerator until growth commences.
The falcifolias are rare in cultivation. Both grasslike seedlings and established plants are entirely deciduous (in western Montana), and do not resume growth until late the following spring. Protected from winter moisture, the desert-dwelling [[Spec.SpecLongiscapa][I. longiscapa
has survived -30 degrees C (-22 degrees F), and appears otherwise as adaptable as regelias to garden cultivation. Falcifolias have not bloomed well in a cool climate, where some clones have slowly increased in size for many years without flowering at all. They may perform more reasonably in warmer, arid soils of southwestern United States.
GROWING ARILS FROM SEEDS
Aril seeds are difficult to germinate naturally because of protracted dormancy. Most people raising arils from seed use embryo culture, or a modified plate culture (Appendix B). These techniques require sterile conditions and great time and effort, but embryos reluctant to germinate under other conditions may yield to such propagation and make possible growing the countless phenotypic variants that may occur among seedlings of some species and hybrids. From these it should be possible to select not only those with more desirable flower form, color and substance, but also clones most adaptable to particular climatic, soil, germination and other conditions.
An additional goal for the aril grower and hybridizer is the development of disease-resistant clones. For example, it is known (Kushnir 1949) that some onco species are especially susceptible to attack by common leaf spot fungi, while other species are partially or completely resistant to infection under the same growing conditions. Likewise, some arils may show signs of mosaic virus infection some years and not others, and a few may exhibit no evidence of infection at all. Thus, by selecting clones for propagation and breeding that are apparently disease-free, breeders may develop arils more resistant to common infectious agents.
DISEASES AND PESTS OF ARILS
Like other iris groups, the arils are hosts to many infectious and parasitic organisms, including leaf spot, rust and other fungi, mosaic virus, nematodes, aphids, whitefly, borers and numerous others. Eradication, prevention or control of these pests is discussed in chaps. 23, 24.
This Chapter (11) is continued with Development of the Arilbred Irises
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