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- Author or Editor: Dermot P. Coyne x
Common bacterial blight, incited by Xanthomonas campestris pv. phaseoli (Xcp), is a serious disease of common bean (Phaseolus vulgaris). RAPD markers and flower color (V gene) previously had been reported to be associated with six QTL affecting leaf and pod resistance to Xcp. However, the markers for the QTL were not confirmed in different populations and environments to indicate their merit in breeding. Our objective was to determine if the associations of RAPD markers and the V gene with QTL for leaf and pod resistance to Xcp in a RI backcross population from the cross BC2F6 `PC-50' × XAN-159 and for leaf resistance to Xcp in a F2 population from a different cross Pinto `Chase' × XAN-159 could be confirmed. Among six QTL previously detected, five in the RI backcross population and three in the F2 population were confirmed to be associated with resistance to Xcp. The V gene and RAPD marker BC437.1050 on linkage group 5 were most consistently associated with leaf and pod resistance to two to five XCP strains in the RI backcross population and with leaf resistance to two Xcp strains in the F2 population. The confirmed marker BC437.1050 and V gene on linkage group 5, along with other resistance genes from other germplasm, could be used to pyramid the different genes into a bean cultivar to enhance the resistance to Xcp.
Genetic variation for abaxial leaf pubescence was detected among dry bean (Phaseolus vulgaris L.) cultivars/lines. Inheritance of pubescence (long, straight hairs) was studied in the dry bean crosses of pubescent `Pompadour Checa-50' (Dominican Republic) × eight glabrous cultivars/lines. Segregation for pubescence vs. glabrousness indicated that pubescence was determined by a single major gene or by duplicate recessive epistatic genes, depending on the cross involved. Trichome density (number trichomes per mm) was a quantitative trait. Thus, pubescence was a discrete trait, but trichome density ranged from low to high.
Expression of lactoferrin (LF) gene, a cationic iron-binding glycoprotein, was investigated in transgenic tomato plants (Lycopersicon esculentum Mill.). Resistance of the transgenic tomato plants to the pathogen (Ralstonia solanacearum Smith) causing bacterial wilt was also determined. Tomato line F7926-96, susceptible to bacterial wilt, was transformed with Agrobacterium strain C58C1 containing a plasmid construction carrying a modified LF cDNA. The introgression of LF cDNA into the susceptible tomato line was confirmed by Southern blot and the expression of full-length lactoferrin transcript and protein was also detected by northern and western blots, respectively. Based on resistance to kanamycin, a Mendelian segregation for a single locus insertion was observed in the T1 and T2 generations and all T1 and T2 plants resistant to kanamycin showed the single corresponding band of LF cDNA in Southern blot analysis. Two transgenic tomato lines inoculated with 1 × 107 and 1 × 108 colony-forming units (CFU)/mL with Rs isolate NC251 (K60, race 1) exhibited early resistance and subsequent susceptibility, while 44% to 55% of plants survived until maturity (fruit ripening) when inoculated with 1 × 105 CFU/mL in comparison with the fully susceptible tomato line. The latter resistance to bacterial wilt in transgenic tomatoes with the stable Mendelian segregation patterns for the LF gene suggests a potential new approach to consider for control of bacterial wilt of tomato. The possible value of this gene along with other plant genes to control bacterial pathogens is discussed.
Dry bean (Phaseolus vulgaris L.) production is limited by bean rust [Uromyces appendiculatus (Pers.) Unger var. appendiculatus]. An effective control strategy for this disease is to breed cultivars with durable resistance. Information on the inheritance, genetic relationships, and mapping of genes with molecular markers for specific resistance (SR), adult plant resistance (APR), and abaxial leaf pubescence (ALP) is needed to pyramid the desired genes for durable resistance. ALP was found to be associated previously with APR in Andean germplasm. The objective here was to identify and map RAPD markers for the genes controlling SR, APR, and ALP and to examine their relationships. Five rust pathotypes were inoculated on the unifoliate leaves of 68 recombinant inbred (RI) lines derived from `PC-50' (presence of SR, APR, and ALP) × XAN-159 (absence of SR, APR, and ALP). SR was determined by a single major gene (Ur-9) to the five rust pathotypes with no detection of recombinants. The fourth trifoliolate leaves were inoculated with one pathotype (A88T1-4b). A single major gene Ur-12 controlled APR to that pathotype. The Ur-9 gene (SR) was independent of and epistatic to the Ur-12 gene (APR). Because of the low number of APR lines in the RI population resulting from the elimination of RI lines with SR, an F2 population was developed from a cross of two homozygous RI lines selected for unifoliate susceptibility to pathotype A88T1-4b and for resistance and susceptibility of the fourth trifoliolate leaves to tag RAPD markers linked to the Ur-12 gene (APR). The single major gene Pu-a determinated ALP and was not linked to Ur-9 (SR) and Ur-12 (ALP). The gene Ur-9 (SR) was linked to RAPD marker J13-1100 at 5 cM and was not assigned to any linkage group or other markers. The gene Pu-a (ALP) was mapped at 20.2 cM from 116.500 and 3.9 cM from marker G3.1150 in linkage group 3. The Ur-12 gene (APR) was mapped at 34.6 cM from marker O13.1350 in linkage group 4b. This is the first report of mapping a gene for APR in common bean.
Seedcoat color is an important trait, as it affects marketing and consumer acceptance of pinto beans (Phaseolus vulgaris L.). Pinto breeding line NE 94-4 showed seedcoat yellowing in on-farm field trials in Nebraska in 1996 and 1997. Hail, sprinkler irrigation, and fall rainfall appeared to be involved in increasing seedcoat yellowing, based on analysis of field and weather data of on-farm trial sites. The objective of this study was to determine the effect of moisture on seedcoat yellowing of pinto line NE 94-4 (susceptible) and pinto `UI-114' (highly resistant). Two greenhouse experiments were conducted involving misting of bean plants near maturity and injecting water into maturing bean pods. Another experiment evaluated the response of seeds of these two bean entries to moisture by placing them on moist filter paper in petri dishes in the laboratory. Results showed that both genotype and moisture content are involved in seedcoat yellowing. This simple, cheap, and effective filter paper test was then used to evaluate seedcoat yellowing of nine pinto genotypes in response to moisture. Pinto NE 94-4 and `Kodiak' showed the greatest change, while `Bill Z' showed the least change, in seedcoat color.
Nine bean cultivars/lines (Phaseolus vulgaris L.) were grown in three soils/rooting media at pH values of 7.9, 6.5, and 5.8 in greenhouse, growth chamber, and field experiments to evaluate the leaf reaction of the plants to a Nebraska bean rust [Uromyces appendiculatus (Pers.) Unger var. appendiculatus] isolate US85-NP-10-1. Significant differences were observed for rust pustule diameter between cultivars/lines grown in the three growth media. Plants grown in the medium at pH 5.8 showed significantly larger rust pustule diameters than those of plants grown at pH 6.5 or 7.9. A significant interaction occurred between growth medium and cultivars/lines for the rust reaction. Concentrations of Cl and Mn in leaves were positively correlated with rust pustule diameter. In contrast, concentration of K in leaves was negatively correlated with rust pustule diameter. Plant breeders attempting to improve beans for rust resistance must consider the growth medium pH in evaluating intensity and severity of rust symptoms on leaves.
Common blight in beans (Phaseolus vulgaris L.), incited by Xanthomonas campestris pv. phaseoli (Smith) Dye, is a serious seedborne disease in various parts of the world. We tried to detect possible differences in seed infection and transmission of bacteria in selected bean cultivars/lines. Dry seeds, flower buds (24 to 36 hr before anthesis), small pods (2 to 3 days old), and green seeds of individual plants of Bac-6, ‘Venezuela 44% ‘Pompadour Checà’ dry beans, and of dry seed of Great Northern (GN) ‘Tara’ were examined for possible internal infection after inoculating the seeds, seedlings, and plants with common blight bacterium at various sites. Inoculation of the pedicels of the flower buds and small pods resulted in transmission of the bacteria through the vascular tissue of the pod to the seeds, causing internal infection without any external symptoms shown either by the pods or seeds. Bac-6 was resistant to seed infection, and ‘Venezuela 44’ was most susceptible, followed by ‘Pompadour Checà’ and GN ‘Tara’. Planting infected seeds did not result in a systemic transmission of the bacteria in the vascular tissue of the plants to the seeds. Infected leaves were likely to be the main source for the external infection of pods, which could lead to internal and/or external seed infection. Breeding for resistance to seed infection and transmission of bacteria should aid the control of this disease. A useful technique for assessing internal infection of seeds with the bacteria was developed.
Seed-coat cracking injury was determined in Great Northern (GN) dry bean lines in 1977, 1978 (also Pintos in 1978) using 3 methods as follows: Vogel small plot thresher (field), seed dropping, and a controlled rotating impact disk machine. Differences in susceptibility for seed-coat cracking were observed within each testing method. Overall, ‘GN Emerson’, near-isogenic determinate ‘GN Nebraska #1’ and ‘Pinto UI 111’ had the best resistance to seed-coat cracking. A genotype × year interaction for seed injury occurred with the Vogel thresher but not with the other 2 methods. The other 2 methods gave consistent results but the rotating disk machine method was preferred because of ease, rapidity of operation and standardization of the rotation speed. The early and late maturing determinate near-isogenic lines of ‘GN Nebraska #1’ had less seed-coat injury than the early and late indeterminate lines using the Vogel and rotating impact disk method. The early determinate line had the least amount of seed-coat injury for all three methods. ‘Pinto UI 111’, ‘Bulgarian White’, and ‘GN D-88’, which exhibited the best resistance to seed-coat cracking in the 7 parent diallel crossing study, had the most uniform seed-coat thickness as well as having thick seed coats. The cultivars which had thin or thick but non-uniformly thick seed coats were susceptible to seed-coat cracking. Differences in thickness in macrosclerid, os-teosclerid and parenchyma cell layers of the seed coat were observed between cultivars, but no relationship between these cell layers and the seed-coat cracking response was established. Seed-coat cracking was quantitatively inherited. ‘Bulgarian White’, ‘Pinto UI 111’ and ‘GN D-88’ showed high combining ability for resistance to seed-coat cracking. The estimates of the genetic effects indicated that additive effects were mainly involved.
A 6-parent Phaseolus vulgaris diallel cross was produced to determine the inheritance of leaf, external, and internal pod reactions to the bacterial pathogen Xanthomonas campestris pv. phaseoli (Smith) Dye = Xanthomonas phaseoli E.F.S. Dows (X.p.) Nebraska isolate EK-11. The parents and F1 generations were grown in the greenhouse, whereas the F2, along with parents, were also grown in the field at 2 locations (Lincoln and Scottsbluff, Neb.). The Gardner and Eberhart (1966) model, Analysis II, was used to obtain estimates of the genetic effects for the reactions to the pathogen in the different plant parts. Coefficients of variation were high in the greenhouse experiment and low in both field experiments. The increased precision of the field experiments allowed more genetic effects to be detected as being significant. The leaves of ‘Great Northern (GN) Nebraska #1 sel. 27’ and Plant Introduction (PI) 207262 were resistant, ‘Tacarigua’ moderately susceptible, and PI 163117, ‘GN 1140’, and ‘Guali’ were highly susceptible. The pods of the first 3 entries, along with ‘GN 1140’ showed moderate resistance, but the internal reaction of the pods of ‘GN Nebr. #1 sel. 27’ showed more susceptibility than the external reaction. The reaction to X.p. was quantitatively inherited in all experiments. Additive effects were primarily involved in the genetic control of the leaf, external, and internal pod reactions to X.p. Heterosis effects for leaf reaction were detected under field conditions. External and internal pod reactions were highly correlated, but little association between leaf and pod reaction was observed. It is, therefore, necessary to select for resistance simultaneously in both plant parts since correlated responses are not expected to be present. Large positive correlations were detected between the reactions of genotypes observed in the greenhouse with those in the field experiments and between the field experiments, indicating that greenhouse tests should adequately predict field performance. A significant genotype × location interaction for leaf reaction was detected, with ‘Guali’ and ‘Tacarigua’ being more susceptible at Lincoln, under higher night temperatures, than at Scottsbluff, indicating the importance of evaluating the reaction of germplasms to this pathogen in different environments.