Gene for broad, contiguous dark stripes in cocozelle squash (Cucurbita pepo)

Alternating intense (dark) and light stripes on the fruits are a fairly common feature of Cucurbita pepo, a highly variable species encompassing various kinds of pumpkins, squash, and gourds. The intense stripes can be narrow and broken or broad and contiguous. Narrow, broken intense striping is conferred by allele l-1 ^St, which is dominant to allele l-1 for non-striped, lightly colored fruits and recessive to allele L-1 for non-striped, intensely colored fruits. Cocozelle-type squash often exhibit broad, contiguous intense stripes. The inheritance of this characteristic was studied by transferring it from cocozelle squash and preparing nearly isogenic lines having broad-striped, narrow-striped, and non-striped light-colored fruits. In the broad-striped near-isogenic line, the intense stripes averaged 37% wider than in its narrow-striped counterpart. The broad-striped line was crossed with the narrow-striped line, the non-striped light-colored line, and the non-striped intense-colored `Fordhook Zucchini'. Broad striping was dominant to narrow striping and to non-striped light and conferred by a single gene; it was recessive to non-striped intense. The gene for broad striping was found to be allelic to that for narrow striping and to that for non-stripe dintense and is herein assigned the symbol l-1 ^BSt. Dominance relationships at the l-1 locus were observed to be L-1>l-1 ^BSt >l-1 ^St >l-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

A recessive,hypostatic gene for plain light fruit coloration in Cucurbita pepo

Summary Fordhook Zucchini, a squash (Cucurbita pepo) cultivar having intensely colored fruits conditioned by genotype D/D L-1/L-1 L-1/L-2, was crossed with Beirut, a squash cultivar having lightly colored fruits. Beirut was also crossed with Vegetable Spaghetti, a cultivar having lightly colored fruits conditioned by genotype d/d l-1/l-1 l-2/l-2, and with tester stocks of genotypes d/d L-1/L-1 l-2/l-2 and d/d l-1/l-1 L-2/L-2. The results indicated that Beirut, like Vegetable Spaghetti, possesses genotype d/d l-1/l-1 l-2/l-2. However, no F₂- or backcross-generation segregates possessing the Light type 1 phenotype, conditioned by recombinant genotype d/d L-1/-l-2/l-2 and heretofore observed when Fordhook Zucchini was crossed with Vegetable Spaghetti, were recovered when Fordhook Zucchini was crossed with Beirut. The results of crossing Beirut with Vegetable Spaghetti and with the tester stocks indicated that both Beirut and Fordhook Zucchini carry a recessive gene, designated pl, which results in Plain light fruit coloration in plants of d/d L-1/- l-2/l-2 genotype. Beirut possesses genotype d/d l-1/l-1 l-2/l-2 pl/pl, Fordhook Zucchini D/D L-1/L-1 L-2/L-2 pl/pl, and Vegetable Spaghetti d/d l-1/l-1 l-2/l-2 Pl/Pl. Both the dominant D allele and the dominant L-2 allele are epistatic to gene pl.Contribution No. 3443-E from the Agricultural Research Organization, Bet Dagan, Israel     

Multiple allelism at a major locus affecting fruit coloration in Cucurbita pepo

The l-2 (light coloration-2) locus in Cucurbita pepo (pumpkin, squash, gourd) has a major effect on fruit color intensity through its complementary interactions with at least three other loci. From a sixth-generation backcross progeny of which a wild gourd having striped fruits was the donor parent and a cultigen having ‘plain light’-colored fruits(genotype l-2/l-2) was the recurrent parent, a true-breeding line was isolated that had a fruit color phenotype that differed from both parents. The fruits of this line were not striped and had a color pattern resembling‘light type 2’ (genotype L-2/–-), but of weaker expression. This newly established line was then crossed with near-isogenic lines of genotypes l-2/l-2 and L-2/L-2 and the resulting filial and backcross progenies were observed under field conditions. The results indicated that the new phenotype is recessive to ‘light type 2’ but dominant to ‘plain light’ and that it is conferred by a single gene. The results of a testcross for allelism indicated that this gene is an allele at the l-2 locus and it is herein designated L-2 ^w. Dominance relationships at the l-2 locus are L-2 > L-2 ^w >l-2. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chromosome location of genes for resistance to powdery mildew in common wheat (Triticum aestivum L.) 1. Mlk and other alleles at the Pm3 locus

Summary Several wheat cultivars/lines were inoculated with isolates of Erysiphe graminis tritici to identify new genes/alleles for resistance. The wheats were tested with 13 isolates that had been characterized from responses on differential lines with known resistance genes. Gene Mlk which occurs in cultivars Kolibri, Syros, Ralle and several other European common wheats was found to be an allele at the Pm3 locus and is now designated Pm3d. The mildew resistance in an old Australian wheat, W150, is conferred by a single gene also allelic to Pm3 and now designated Pm3e. The near-isogenic line Michigan Amber/8^*Cc possesses another allele now designated Pm3f. A Syrian land variety of common wheat shows mildew resistance that is conditioned by the combination of genes Pm1 and Pm3a. Finally, two accessions of Triticum aestivum ssp. sphaerococcum appeared to possess the Pm3c allele.     

Expression of late maturity α-amylase in wheat containing gibberellic acid insensitivity genes

Summary Two wheat cultivars, Spica and Lerma 52, which consistently produce high levels of -amylase during the later stages of grain development (late maturity -amylase), were crossed with a set of four near-isogenic lines carrying the tall (rht) allele or one of the dwarfing genes Rht1, Rht2 or Rht3 (GA-insensitive alleles). The F₁ and F₂ populations were developed and analysed for grain -amylase and plant height. The Rht3 gene exhibited the strongest influence on plant height and strongly inhibited new -amylase synthesis during the later part of grain ripening. By comparison, Rht1 and Rht2 had a less pronounced effect but still significantly reduced the expression of late maturity -amylase. These observations suggest that gibberellic acid is involved either directly or indirectly in this phenomenon. The implications of the effect of dwarfing genes on expression of late maturity -amylase are discussed in relation to cultivar improvement and to the identification and control of high -amylase germplasm.     

The inheritance of white fruit and stem color in summer squash Cucurbita pepo L.

Summary White fruited plants from the variety White bush were crossed to green and striped fruit in order to study the inheritance of white fruit in summer squash. The genetic ratio suggested that green fruit is controlled by two genes, C and R, and that one (C) has a dominant epistatic control. The white fruit is determined as ccrr. A third fruit color group appeared in the F₂, F₃ and BC₁, having white fruit after anthesis which changed to green during development. The genetic control for this fruit is suggested to be ccR..The green striped fruit showed a simple dominance (St) over the plain white.The dark stem of the Zucchini variety showed single gene dominance (D) over the light green stem.It was found that an association exists between the nonpersistent fruit color and dark green stem, and between white fruit and light green stem.Contribution from the Volcani Institute of Agricultural Research, Bet Dagan, Israel. 1968 Series; No. 1437E.     

Mutations blocking sensitivity to gibberellic acid promote ethylene-induced male sterility in wheat

Summary Ethylene is known to perturb normal reproductive development in wheat, particularly the development of functional pollen. Two experiments were carried out to test the hypothesis that increasing insensitivity to gibberellic acid (GA), conferred by the Rht genes, would be associated with increased male sterility in ethrel or Cerone^®-treated wheat. Wild type (WT=rht1/rht1, rht2/rht2), single dwarf (SD=Rht1/Rht1, rht2/rht2 or SD=rht1/rht1, Rht2/Rht2), and double dwarf (DD=Rht1/Rht1, Rht2/Rht2) near-isogenic lines in six genetic backgrounds were treated with ethrel or Cerone^® at the late tetrad to early uninucleate stage of pollen grain development. Ethrel induced pollen abortion in all genotypes but was highest for DD (41% above background) followed by SD (20%), and then WT genotypes (10%). Spikelet fertility decreased as the number of Rht alleles increased in response to ethrel or Cerone^® treatments. Expressed as a percent of controls, spikelet fertility was 56% for WT, 42% for SD, and 29% for DD. The consistent linear relationship between the number of Rht alleles and sensitivity of ethylene-induced male sterility suggests that GA and its recognition may exert a stabilizing effect in pollen development in the presence of stress or an ethylene shock.Paper No. 764 of the Department of Plant Breeding and Biometry, Cornell Agricultural Experiment Station.     

Oil content, tocopherol composition and fatty acid patterns of the seeds of 51 Cannabis sativa L. genotypes

The oil content, the tocopherol composition, the plastochromanol-8 (P-8) content and the fatty acid composition (19 fatty acids) of the seed of 51 hemp (Cannabis sativa L.) genotypes were studied in the 2000 and 2001 seasons. The oil content of the hemp seed ranged from 26.25% (w/w) to 37.50%. Analysis of variance revealed significant effects of genotype, year and of the interaction (genotype × year) on the oil content. The oil contents of the 51 genotypes in 2000 and 2001 were correlated (r = 0.37**) and averaged 33.19 ± 1.45% in 2000 and 31.21 ± 0.96% in 2001. The -tocopherol, -tocopherol, -tocopherol, P-8- and -tocopherol contents of the 51 genotypes averaged 21.68 ± 3.19, 1.82 ± 0.49, 1.20 ± 0.40, 0.18 ± 0.07 and 0.16 ± 0.04 mg 100g^–1 of seeds, respectively (2000 and 2001 data pooled). Hierarchical clustering of the fatty acid data did not group the hemp genotypes according to their geographic origin. The -linolenic acid yield of hemp (3–30 kg ha^–1) was similar to the -linolenic acid yield of plant species that are currently used as sources of -linolenic acid (borage (19–30 kg ha^–1), evening primrose (7–30 kg ha^–1)). The linoleic acid yield of hemp (129–326 kg ha^–1) was similar to flax (102–250 kg ha^–1), but less than in sunflower (868–1320 kg ha^–1). Significant positive correlations were detected between some fatty acids and some tocopherols. Even though the average content of P-8 in hemp seeds was only 1/120^th of the average -tocopherol content, P-8 content was more closely correlated with the unsaturated fatty acid content than -tocopherol or any other tocopherol fraction. The average broad-sense heritabilities of the oil content, the antioxidants (tocopherols and P-8) and the fatty acids were 0.53, 0.14 and 0.23, respectively. The genotypes Fibrimon 56, P57, Juso 31, GB29, Beniko, P60, FxT, Félina 34, Ramo and GB18 were capable of producing the largest amounts of high quality hemp oil.     

A rapid procedure for screening the resistance of bean cultivars (Phaseolus vulgaris L.) to Botrytis cinerea and Sclerotinia sclerotiorum

Summary A method to inoculate detached bean leaves with Botrytis cinerea or Sclerotinia sclerotiorum without using a carbon-nitrogen source is described. Leaves were incubated in plastic trays that were covered with transparent plastic bags to maintain air humidity above 95%. Spores of either fungus inoculated in water alone were generally unable to cause infection. Additions of KH₂PO₄ (62.5 mM) or of mixtures of inorganic phosphate and glucose (1.1 or 5.5 mM) to the inoculum stimulated fungal pathogenicity. Also spore concentration (2×10⁵ or 2× 10⁶ spores ml^–1) influenced the ability to produce lesions. At 2× 10⁶ spores ml^–1 both fungi were able to infect primary bean leaves when inoculated in an inorganic phosphate solution. These conditions were used for a preliminary screening for resistance of 15 bean cultivars to both fungi. Only partial resistance to the pathogens was found. Since the procedure is simple and does not require blooming plants, it can be rapidly adopted in screening and breeding programs.Abbreviations Pi inorganic phosphate     

Correlation between α-amylase gene expression and seedling vigor in rice

Summary This report examines the relationship between seedling vigor, -amylase enzyme activity and -amylase mRNA accumulation in ten varieties of rice (Oryza sativa L.) grown at two temperatures (15°C and 30°C). A significant, positive correlation was observed between seedling vigor, -amylase enzyme activity, and the accumulation of mRNA from one rice -amylase gene (RAmy1A) at both temperature regimens. The results of this study support previous experiments which have correlated -amylase enzyme activity to seedling vigor. We have extended this correlation to the expression of one of ten genes that comprise the rice -amylase multigene family. These results suggest that the expression of -amylase gene RAmy1A is an important, and possibly rate-limiting factor in determining seedling vigor in rice.     

Selection from Solanum tuberosum group phureja of genotypes combining high-frequency haploid induction with homozygosity for embryo-spot

Summary In this article the term pollinators refers to diploid genotypes of Solanum tuberosum Group Phureja which are used to pollinate autotetraploid potatoes for the induction of autonomous growth of unfertilized egg cells. Plants obtained from such egg cells contain chromosomes of the female only and are called dihaploids. The successful selection of ideal pollinators from Group Phureja is described. A pollinator is considered to be ideal, if it has good male fertility, homozygosity for the dominant seed marker embryo-spot and the ability to induce in autotetraploid cultivars a high number of dihaploids both per berry and per 100 seeds. Embryo-spot is a deep purple or reddish coloration at the base of the cotyledons of the embryo, visible on both sides of the flat seeds. It is one manifestation of a set of complementary genes with pleiotropic action, causing a concentration of anthocyanins at the base of all plant organs that are homologous to leaves. The complementary genes are: a basic gene P for anthocyanin production (this is the seedling marker coloured hypocotyl) and allele B ^d of locus B. Thirty-three homozygous B ^d B ^d PP plants and 41 B ^d bPP plants were identified and a number from both classes tested as pollinator onto varieties.Among the homozygous group a number of ideal pollinators could be detected. Unexpectedly a few polyploids grew from spotless seeds when using homozygous pollinators on varieties; 1.4% showed purple hypocotyl and 2.6% were matroclinous. The latter group of polyploids probably may have arisen from unreduced egg cells of the cultivars used.In the progenies from crosses between recessive cultivars (bbbbpppp) and heterozygous pollinators (B ^d bPP) the ratio of spotted: spotless hybrid seeds appeared to deviate greatly from 1:1. This is ascribed to unreduced gametes, which originate during meiosis, presumably through lack of formation of the reductional (= first division) cell wall. On this assumption a map distance of 30 and 24 cross-over units is estimated for locus B on the basis of the proportion of nulliplex tetraploid hybrids in two different crosses.High- and low-seed-set pollinators were found at a ratio of 8:21 suggesting monogenic dominance of low seed-set. Seeds per berry and haploids per berry are significantly correlated using low-seed-set pollinators on cultivars, but they are not when pollinators are used that produce high numbers of seeds per berry. A hypothesis is put forward to explain this phenomenon.     

Effect of genetic blends of dry beans (Phaseolus vulgaris) of different Plant architecture on apothecia production of Sclerotinia sclerotiorum and white mold infection

Summary The determinate Phaseolus vulgaris L. cvs Dark Red Kidney Charlevoix, and near-isogenic Great Northern Nebraska 1 were grown in blends with the indeterminate GN Nebraska 1 in white mold (Sclerotinia sclerotiorum) disease field nurseries. A critical difference between Charlevoix and indeterminate GN Nebraska 1 is that the latter has a greater leaf area closer to the soil surface, and this is associated with increased numbers of apothecia beneath the canopy and higher disease severity. White mold infection and apothecia number/m² beneath the canopy of the blends containing Charlevoix were significantly reduced in comparison with the severely infected, homogeneous, indeterminate GN Nebraska 1. A reduction of white mold infection for the indeterminate GN Nebraska 1 was not observed in blends grown under severe or moderate white mold incidence, but did occur under slight incidence in blends containing 65% and 75% Charlevoix.No significant difference for seed yield occurred between the blends and homogeneous cultivars planted in four experiments under severe, moderate, slight and zero white mold incidence, respectively, except in Experiment 1 under moderate white mold incidence, the blend of 50% indeterminate GN Nebraska 1 and 50% Charlevoix exceeded the yield of the indeterminate GN Nebraska 1. Mean weight of white (GN Nebraska 1) and red seed (Charlevoix) increased and decreased, respectively, in some blends due to the more vigorous growth of the indeterminate GN Nebraska 1.Published as Paper No. 5341, Journal Series, Nebraska Agric. Exp.t Station. Research was conducted un under Project 20–3.     

Genetic variation for resistance to Phytophthora fragariae var. rubi in red raspberries

Summary The inheritance of root rot resistance in red raspberry, caused by Phytophtora fragariae var. rubi, was investigated using two experimental breeding designs. Design A was not randomly mated and genetic parameters could not be calculated. Design B was therefore randomly mated to make it possible to do such estimations. Considerable genetic variation was associated with the recorded traits on seedlings tested in a glasshouse. Disease index and % survival were both found to be highly heritable with broad sense heritabilities (H²) close to 0.9 in each design. Estimates of narrow sense heritability (h²), indicated that progress towards resistance would be moderate. In the first design the cultivars Festival, Asker, Boyne and Sentry and the clones N85-02-13 and N85-06-140 had high general combining abilities. Some crosses had a high specific combining ability indicating the presence of non-additive genetic variation.     

Chromosome locations of genes controlling ‘purple leaf base’ in rye and wheat

Summary Purple leaf base is expressed only if there is anthocyanin pigmentation in coleoptiles either in rye or in rye-wheat-additions. Genes controlling purple leaf base were found to be located on chromosomes 5R (An5), 4B (Ra2) and 6B (Ra3) using the trisomic set of rye cv. Esto and autoplasmic rye-wheat-additions, respectively.     

Effects of the Russian wheat aphid on osmotic potential and fructan content of winter wheat seedlings

Summary The effect of an autumn Russian wheat aphid, Diuraphis noxia (Mordvilko), infestation on winter wheat, Triticum aestivum L., was investigated using osmotic potential, fructan content and field survival measurements to estimate coldhardiness. An average infestation of 147 aphids per plant, under simulated hardening conditions, increased the osmotic potential of Froid and Brawny (more or less coldhardy varieties, respectively) seedlings by 0.236 and 0.345 MPa, respectively. A natural field infestation averaging 9.7 aphids per plant reduced fructan contents of Froid and Brawny seedlings by 22.60 and 59.10 g kg^-1 dry wt., respectively. Similar trends occurred after a natural freeze period. Field survival and yield results indicate that the autumn infestation reduced the winter survivability of Brawny by 54% and reduced grain yields by 1217 kg ha^-1; survival and yield of infested Froid were not significantly affected. PI 372129, a D. noxia resistant winter wheat genotype was not affected by an infestation in regard to these parameters. These studies suggest that coldhardiness in Froid and Brawny was reduced by D. noxia though only the less hardy Brawny had a significantly reduced winter survivability and grain yield. Therefore, the effects of an autumn D. noxia infestation on some winter wheat genotypes may interact with a winter climate and increase the potential for winterkill.     

Slow-growth conservation of potato microplants: efficacy of ancymidol for long-term storage in vitro

Ancymidol was investigated as an alternative mediumsupplement to mannitol for slow-growth conservation ofpotato microplants in vitro. Differentconcentrations of ancymidol (0, 5, 10, 15, 20, 25, 30,35 and 40 M) were tested in slow-growthmedia based on MS medium supplemented with either 30or 60 gl^-1 sucrose. The cultures were conservedunder a 16-h photoperiod at two temperature regimesi.e. 24 ± 1 ^°C and 6 ± 1 ^°C. Therewere significant interactions between ancymidol andother factors such as sucrose, temperature andgenotype for microplant survival, microshoot heightand overall microplant growth. Ancymidol did have abeneficial effect on culture viability after prolongedmaintenance in vitro. The growth-inhibitingeffect of ancymidol persisted through a 16-monthculture period. Combined effect of ancymidol, sucroseand temperature showed that optimum culture viabilityand desirable microplant growth were obtained when thecultures were grown in MS medium supplemented with 10M ancymidol plus 60 gl^-1 sucrose at6 ± 1 ^°C. Vitrification and flaccidity, whichare very frequently observed in potato microplantcultures during prolonged maintenance in vitrounder osmotic stress (mannitol), were not observedwhen the microplants were conserved in ancymidolmedia. Genetic stability of potato microplantsconserved in ancymidol media was evaluated usingrandomly amplified polymorphic DNA (RAPD)fingerprints. Ancymidol did not induce any detectablegenetic variation in genomic DNA as visualized by theabsence of either any additional RAPD fragment oralterations in RAPD fragment patterns.     

α-Tomatine and other steroidal glycoalkaloids in fruits of tomato lines resistant to the glasshouse whitefly (Trialeurodes vaporariorum Westw.)

Summary The total steroidal alkaloid compositions of the mature-harvested fruits of the tomato cultivar Allround (Lycopersicon esculentum), of the species L. hirsutum glabratum, resistant to the glasshouse whitefly (Trialeurodes vaporariorum), and of four resistant lines were determined by capillary gas chromatography. The contents of -tomatine in the red-ripe fruits of Allround and in those of the lines were low (5 mg/kg fresh weight). The green-mature fruits of the wild species had a high content (3390 mg/kg fresh weight) of -tomatine. The total alkaloid profiles of Allround and of the lines were similar. Comparison of flame ionisation detector response with thermoionic detector response indicated that in addition to tomatidine, the aglycone of -tomatine, a small amount of one other steroidal alkaloid might be present in Allround and in the lines. The wild species contained five compounds which possibly are steroidal alkaloids.The safety level of -tomatine in tomatoes is discussed. It was concluded that, in respect of the glycoalkaloids of the mature-harvested fruits, the resistant tomato breeding lines are as safe for human cosumption as the standard cultivar.     

Selection for early flowering in progenies of interspecific crosses of ten species in the genus Dianthus

Summary Twenty-seven progenies of interspecific crosses, involving ten Dianthus spieces (D. caryophyllus, D. chinensis, D. superbus, D. barbatus, D. japonicus, D. brachyzonus, D. versicolor, D. trifasciculatus, D. serotinus and D. knappii) and some complex interspecific hybrids (Diantini genotypes and D. Allwoodii selections) were grown from seed under 8 hr days at two light intensities: 12 W/m² and 22 W/m². Observations on individual plants were made on vegetative development and date of flowering. After six months, 178 plants were selected from 23 seedling progenies and the resulting clones were compared under 22 W/m² and two photoperiods: 8 hrs and 24 hrs per day for a period of nearly six months. In the seedling stage, large differences were observed between progenies, e.g. in percentage generative plants (0–100%), plant length (3–78 cm) and plant fresh weight (0.5–68 g). Effects of light intensity were most pronounced in plant fresh weight (0.2–18 g in 12 W/m² and 0.5–68 g in 22 W/m²). Progenies of D. chinensis were the earliest to flower. Most progenies of crosses between D. superbus and D. barbatus segregated into flowering and non-flowering (rosetting) plants. In the clonal stage, most clones originating from non-flowering seedlings remained vegetative (rosetting), while all clones from flowering seedlings were either in flower or in bud within six months. Average dates of flowering of seedling progenies and of their clones were highly correlated, suggesting that selection on flowering date at the seedling stage is effective. High correlations were also found between the average flowering date of seedling progenies and the number and total weight of flowers harvested per plant in their clones within six months from planting. Overall effects of LD in the clonal stage were much less spectacular than the effects of light intensity in the seedling stage.     

Genotyping-by-sequencing of waxy and glossy near-isogenic broccoli lines

Wild-type Brassica oleracea L. have matte blue-green leaves caused by an interaction between leaf pigmentation and a waxy bloom coating the surface. Glossy mutants have reduced and/or altered epicuticular wax giving the leaves a shiny green appearance and have been identified in most B. oleracea crop varieties, including cauliflower, kale, broccoli, Brussels sprouts, cabbage, and collard. The genetic basis of glossy mutants has not been studied in B. oleracea. Glossiness can confer resistance to multiple herbivores mediated by modification of herbivore feeding behavior and foraging efficiency of their predators. The USDA-ARS-U.S. Vegetable Laboratory released two pairs of near-isogenic broccoli lines (NILs) that visibly differ only for glossiness, providing ideal germplasm for the genetic study of epicuticular wax in B. oleracea. Genotyping-by-sequencing resulted in hundreds of polymorphisms between each pair of NILs. Polymorphisms were identified in or near three different wax synthesis genes suggesting the two glossy mutants were caused by alteration of different steps of the pathway.     

Resistance of wild emmer wheat to stem rust: Ecological,pathological and allozyme associations

Summary Seedling resistance to wheat stem rust was determined in populations of wild emmer wheat, Triticum dicoccoides, and characterized by means of ecological factors and allozyme genotypes. Reactions to wheat stem rust were studied in 102 single plant accessions of T. dicoccoides from ten populations by inoculation with Puccinia graminis tritici race 14, isolate GSR-739. Six populations displayed different degrees of response polymorphism with reactions ranging from high resistance to complete susceptibility, whereas four populations contained only susceptible plants. In some of the accession, unexplained intrasib variation in resistance and intraplant variation of infection-types were found. Resistance to stem rust was negatively correlated with two ecological factors, altitude and number of Sharav (hot-dry) days which are unfavorable to disease development. Variation in stem rust response was shown to exist in ecogeographic regions where climatic variables enhanced the development of the fungus, conceivably maintained by natural selection. Likewise, allozyme genotypes, single or in multiple loci combinations, appeared to be associated with resistance or susceptibility to rust. Such association need to be verified by genetic studies in order to become established as useful markers.