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Procedures were developed to permit screening pistachio for resistance to infection by Botryosphaeria dothidia panicle and shoot blight. A method of growing B. dothidea in liquid culture was developed and two inoculation procedures, direct injection of inoculum into shoots at the base of leaf petioles and a leaf scratch assay, were used to test selected pistachio (Pistacia vera L.) clones for resistance to B. dothidea. Both the direct injection and the scratch test procedures provided easily scored symptoms. Both solid and liquid cultures produced visible infections. Sources of resistance were identified in an F1 interspecific P. vera cv. Sfax × P. integerrima hybrid cross and P. integerrima genotypes. P. integerrima may be a valuable source of resistance for cultivar improvement, but resistant P. vera genotypes were not found. No correlation between Alternaria alternata resistance and B. dothidea resistance was found in P. vera.
Four pistachio rootstocks, Pistacia atlantica, P. integerrima, and two selections of the same interspecific hybridization, P. atlantica, P. atlantica × P. integerrima (A.K.A. PGII and UCB #1) budded with P.vera, P. vera cv. Kerman females have been evaluated since 1989 in three locations in California's central San Joaquin Valley. Thus far, Atlantica is the most cold tolerant, followed by the interspecific hybrids and Integerrima. Integerrima and UCB no. 1 have produced significantly more clusters and nuts per tree, but all rootstocks have produced the same numbers of nuts per cluster. Trees on no.1 and Integerrima rootstocks also have produced significantly more kilograms of nuts per trunk cross sectional area than Atlantica and PGII. UCB #1 and Integerrima also are significantly more tolerant of the soilborne fungus Verticillium dahl. All rootstocks are equally infected with three species vesicular–arbuscular mycorrhizzae. Two seasons of irrigation with water up to 8.00 dS·m–2, have not affected rootstock performance or yield. UCB #1, Integerrima, and PGII all require supplemental boron, zinc, and copper nutrition for good production. Thus far, Integerrima is the best rootstock for soils with verticillium infestations unless winter temperatures are frequently below freezing. UCB #1 is the best rootstock for locations with cold winters.
The methods of Wall and York (1957) were used to measure cotyledon position in two populations of three species interspecific Phaseolus hybrids and in the single species cultivars and accessions of P. coccineus, P. acutifolius, and P. vulgaris used as parents. Cotyledon position was represented by the length of the epicotyl as a percentage of the total length of the seedling's stem from the first root initial to the base of the primary node. Progeny of interspecific crosses between P. coccineus and P. vulgaris have been shown to inherit the cotyledon position of the cytoplasmic parent. The objectives of this study were to determine if three species hybrids also inherited the cotyledon position of the cytoplasmic parent, and to determine if P. acutifolius could be distinguished from P. vulgaris by its cotyledon position. Results indicated that the cotyledon positions of the three species hybrids did not differ significantly from the cotyledon positions of cultivars of the species used as the cytoplasmic parent for both P. vulguris cytoplasm and P. coccineus cytoplasm. Further, the cotyledon position of the P. acutifolius accessions did differ significantly from the cotyledon positions of both the P. vulgaris cultivars and the three species hybrid with P. vulgaris cytoplasm. These results suggest that cotyledon position may indeed be a species-specific trait for Phaseolus in Lamprecht's sense of the term.
The grape belongs to the genus Vitis L., which are divided into two subgenera, Euvitis Planch. and Muscadinia Planch. The Euvitis has 50 to 70 species, in which V. vinifera L. is a predominant species with hundreds of known commercial cultivars grown world wide. The Muscadinia (muscadine grapes) consists of only two to three species predominated by V. rotundifolia and only commercially cultivated in the southeastern United States. V. rotundifolia is known by its multiple resistance to almost all grape diseases and insects found on the Euvitis species, while the latter possesses good fruit characteristics that do not exist in muscadines. Attempts to produce rotundifolia-vinifera hybrids to combine good fruit quality and disease resistance of both into F1 hybrids have been made by grape breeders for many years. Limited success was reported when the V. vinifera was used as seed parents. This research extended the interspecific crosses beyond V. vinifera into other Euvitis species. Among the Euvitis species, A. aestivalis, V. cinerea, V. champinii, V. labrusca, V. monticola, V. nesbittiana, V. riparia, V. rupestris, V. thunbergii, V. quinguangularis, all with pistillate flowers, were used as female parents pollinated with V. rotundifolia pollen. Eight out of the 10 cross combinations except V. cinerea and V. thunbergii set fruits. However, most of the Euvitis-rotundifolia crosses had extremely low fruits set (<1% of pollinated flowers). The only exception was V. labrusca cv. Woodruff, which had very high percentage of fruit set (70%). Interestingly, the fruits of V. labrusca cv. Woodruff × rotundifolia were pathonocarpic that had only half size of regular fruits set from open pollination with pollen sources from other Euvitis species. In the reciprocal crosses, three pistillate V. rotundifolia cultivars, `Fry', `Higgins', `Jumbo', were used as female pollinated by pollen from Euvitis species. Limited fruit sets were found from the crosses of V. rotundifolia × V. shuttleworthii, V. cordifolia, V. rupestris, V. Piasezkii, V. quinquagularis. Results from this study indicated that hybridization between Euvitis and muscadinia species is indeed very difficult but it is possible, and some Euvitis species are cross more compatible with V. rotundifolia than the others.
Central Asia is the center of origin for many Allium species and a rich genetic source of wild relatives of onion and garlic. For this reason germplasm collections of cultivated Alliums have targeted the acquisition of seed and bulb samples from this region, and several plant expeditions from Asia, Europe, and North America have collected Allium germplasm in Central Asia. Central Asian Allium germplasm has been valuable both as raw materials for scientific research leading to published data, and as starting materials for genetic improvement of the crop. Utilizing this germplasm it has been possible to improve garlic so it can be bred like other seed-propagated crops. Several interspecific crosses have been made between onion and other Central Asian wild relatives and these crosses have yielded useful traits for onion improvement. Allium germplasm from this region has also been important in elucidating the systematics and origins of diversity in onion and garlic. By any of these measures, Central Asian Allium collections have been valuable. Challenges and successes in collecting, maintaining, evaluating, and using these collections remain.
Traditional and biotechnological breeding techniques are being united to develop exciting new plants and to improve existing cultivated plants by introducing natural variability from germplasm resources. Intervarietal, interspecific and intergeneric crosses can be accomplished by using plant embryo culture techniques, sometimes also referred to as embryo rescue. Embryo culture involves the isolation and growth of immature or mature zygotic embryos under sterile conditions on an aseptic nutrient medium with the goal of obtaining a viable plant. The technique depends on isolating the embryo without injury, formulating a suitable nutrient medium, and inducing continued embryogenic growth and seedling formation. The culture of immature embryos is used to rescue embryos from hybrid crosses that were once thought to be incompatible because they would normally abort or not undergo the progressive sequence of ontogeny. The culture of mature embryos from ripened seeds is used to eliminate seed germination inhibitors, to overcome dormancy restrictions, or to shorten the breeding cycle. New and exciting cultivars of Alstroemeria, also known as Lily-of-the-Incas, Inca Lily, or Peruvian Lily, have been bred by using zygotic embryo culture; these techniques and applications will be discussed.
Nineteen interspecific hybrid breeding lines were tested for resistance to a TSWV isolate using enzyme-linked immunosorbent assay (ELISA) to check for presence of the virus after inoculation. These lines were all BC1F6 lines derived from L. esculentum crosses with seven L. chilense accessions. All of these lines had been selected for high tolerance/resistance to tomato mottle virus (ToMoV), a geminivirus [Scott et al., Bemisia 1995: Taxonomy, Biology, Damage Control and Management 30: 357–367 (1996)]. The initial TSWV screening indicated that eight of the 19 original lines had “possible” TSWV resistance. Seed from these selected eight lines were then planted and inoculated with TSWV ≈3 weeks after emergence. Three weeks later, ELISA results indicated that all plants from all lines were infected with TSWV. However, none of the plants from Y118 (derived from the LA 1938 cross) showed visual TSWV symptoms. The Y118-derived plants were allowed to grow for several months, and at no time developed significant visual symptoms of the virus. The consistent lack of TSWV symptoms prompted a second ELISA test on the Y118 plants, and the results indicated the plants were completely free of TSWV. Further tests were then initiated with F2 (L. esculentum × Y118) seed, and results indicate a single dominant gene is responsible for TSWV resistance. Data from this segregating population, including a molecular marker study which screened 800 randomly amplified polymorphic DNA (RAPD) primers, will be presented. Approximately two to five RAPD primers are possibly linked to TSWV resistance.
The genus Aesculus (buckeyes and/or horsechestnuts) is composed of 13 species and a number of interspecific hybrids. Pollen from 11 genotypes from five Aesculus species and the hybrid Aesculus ×carnea were used to develop an in-vitro germination test to evaluate pollen viability under various storage treatments. This test was optimized using samples of both fresh pollen and pollen that had been stored up to 1 year. The most effective medium contained 20% sucrose, 100 mg·L-1 H2BO3, 150 mg·L-1 Ca(NO3)2, and 1% agar. The highest germination percentage was observed at 15 °C across all storage treatments. Fresh pollen germinated in excess of 80% over a wide range of germination temperatures. Based on this, all specimens studied would be good pollen parents. The differences in pollen germination between storage at -20 and -80 °C were nonsignificant, but the duration of the storage period was highly significant. At 3 months, viability remained above 60% for four of the six species/hybrid tested. However, at 12 months, all pollen tested dropped below the threshold for good fruit set based on in-vitro pollen germination. Based on these observations, short-term pollen storage may permit crosses between parents with temporally separate flowering phenologies. However, conventional storage procedures are inadequate to maintain pollen collected from a male parent for crosses in subsequent growing seasons.
Pepper (Capsicum spp.) has the same basic chromosome number as tomato and other solanaceous plant species (2n = 2x = 24). By using the probes mostly from a tomato map, we have generated three molecular maps of pepper from interspecific F2 crosses of C. frutescens BG 2814-6, C. chinense PI 159234 and C. annuum `NuMex RNaky' with restriction fragment length polymorphisms, isozymes, random amplified polymorphic DNAs, and morphological traits. The best developed map is from C. annuum × C. chinense F2 cross, which currently has 366 markers covered 1081 cM in 18 linkage groups. Three linkage groups were assigned to three chromosomes based on primary trisomics. Several disease resistance genes including monogenic resistance to potyviruses and quantitative trait loci for resistance to tobacco mosaic virus and cucumber mosaic virus have been mapped. The distribution of allele frequency and marker segregation ratios have been analyzed. Chi-square analyses of all clones showed more skewing of segregation ratios in C. annuum × C. chinense population than the other two populations. The skewing occurs throughout the genome and tends towards heterozygote and one of the parents. The order of markers among three pepper maps will be compared and the comparisons of synteny between pepper and tomato maps will be described. A composite of three pepper maps will be presented using JoinMap software.
Little is known about the mechanisms controlling interspecific barriers, unlike the well studied intraspecific barrier, self incompatibility (SI),. A unilateral crossing barrier (unilateral incongruity - UI) exists among the Lycopersicon species, in which crossing is impeded or prevented in one direction. Since both UI and SI can give unilateral differences in seed set, suggestions have been made that UI and SI are functionally related. L. pennellii LA716 is self-compatible, unlike the other accessions which are SI, but LA716 still exhibits UI with L. esculentum (esc). We observed the development of pollen tubes in self and cross pollinations of LA716, esc and SI accessions of L. pennellii (pen). Selfed pollen tubes in esc were at the ovary in 24 hours, while pen were 1/2 way down the style and in LA716 the pollen had not germinated. By 48 hours, the pollen tubes in LA716 were in the ovary and growth had halted in pen styles. Crosses with LA716 pollen on esc and pen resulted in pollen tube growth starting within 24 hours continuing to the ovary. Thus, UI is not a SI response and LA716 shows a delayed pollen germination and growth unlike the other Lycopersicon species examined.