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- Author or Editor: James D. Kelly x
Field experiments were conducted at two locations in Puerto Rico to measure the effect of growth habit on the ability of bean (Phaseolus vulgaris L.) genotypes to compensate for variation in plant population in hill-plots. Five determinate and five indeterminate bean genotypes were grown in 1-m-diameter hill-plots ranging in population from two to 10 plants per hill-plot. The indeterminate genotypes produced a greater seed weight per hill-plot, a smaller 100-seed weight, a greater number of pods per plant, and a greater number of seeds per pod than the determinate genotypes. Number of seed per pod and 100-seed weight did not differ significantly as the number of plants decreased from 10 to two plants per hill-plot. Number of pods per plant and seed yield per hill-plot increased in a linear fashion as the number of plants per hill-plot decreased. A covariance analysis using number of plants per hill-plot as the cov-ariate would be appropriate for adjusting hill-plot yields for variation in plant population. The similarity of the seed yield response of determinate and indeterminate bean genotypes to varying population density would permit both habits to be analyzed in a single covariance analysis.
Root rot, caused by Fusarium solani f.sp. phaseoli, is a serious disease of bean for which successful control has been elusive. Genetic resistance to the pathogen is considered quantitative and is strongly influenced by environmental factors. To reduce environmental variation and facilitate selection in earlier generations, an accurate, consistent, and nondestructive greenhouse screen was developed for the evaluation of Fusarium root rot resistance in bean. We describe a protocol that involves the germination of seedlings in perlite, inoculation of roots and hypocotyls 10 days after planting and evaluation within 4 weeks. The accuracy of this greenhouse screen was confirmed by demonstrating significant correlations between greenhouse and field ratings. Two experiments that included 24 and 21 diverse bean genotypes, respectively, were performed in the greenhouse and the ratings were correlated with field ratings over two growing seasons. Correlation coefficients between the greenhouse and field ratings were significant and as high as 0.99. Numerous genotypes can be evaluated within a short time for relatively minimal costs and labor. Furthermore, once roots have been rated and dipped in fungicide, plants can be transplanted for production of seed. This simple, rapid, and inexpensive protocol reduces environmental variation inherent to field ratings, thereby more accurately representing physiological resistance while maintaining a close association with observed field ratings.
Resistance to anthracnose in common bean is conditioned primarily by nine major independent genes, Co-1 to Co-10 as the Co-3/Co-9 genes are allelic. With the exception of the recessive co-8 gene, all other nine are dominant genes and multiple alleles exist at the Co-1, Co-3 and Co-4 loci. A reverse of dominance at the Co-1 locus suggests that an order of dominance exists among individual alleles at this locus. The nine resistance genes Co-2 to Co-10 are Middle American in origin and Co-1 is the only locus from the Andean gene pool. Seven resistance loci have been mapped to the integrated bean linkage map and Co-1 resides on linkage group B1; Co-2 on B11, Co-3 on B4; Co-4 on B8; Co-6 on B7; and Co-9 and Co-10 are located on B4 but do not appear to be linked. Three Co-genes map to linkage groups B1, B4 and B11 where clusters with genes for rust resistance are located. In addition, there is co-localization with major resistance genes and QTL that condition partial resistance to anthracnose. Other QTL for resistance may provide putative map locations for the major resistance loci still to be mapped. Molecular markers linked to the majority of major Co-genes have been reported and these provide the opportunity to enhance disease resistance through marker-assisted selection and gene pyramiding. The 10 Co-genes are represented in the anthracnose differential cultivars, but are present as part of a multi-allelic series or in combination with other Co-genes, making the characterization of more complex races difficult. Although the Co-genes behave as major Mendelian factors, they most likely exist as resistance gene clusters as has been demonstrated on the molecular level at the Co-2 locus. Since the genes differ in their effectiveness in controlling the highly variable races of the anthracnose pathogen, the authors discuss the value of individual genes and alleles in resistance breeding and suggest the most effective gene pyramids to ensure long-term durable resistance to anthracnose in common bean.
Common beans, considered sensitive to moisture stress, are an important commodity in developing countries such as the Mexican Highlands where intermittent drought conditions are prevalent during the growing season. The selection and development of high performing cultivars under drought stress is confounded by the quantitative nature of drought tolerance. To employ indirect selection in earlier generations, RAPD markers were identified that associated with QTLs controlling performance under drought stress. RAPD markers are preferred for use in Phaseolus vulgaris, over RFLPs, because they generate polymorphisms between genetically related germplasm. 48% of 620 arbitrary primers screened against three parents of two F6 derived recombinant inbred pinto populations were polymorphic for one or more bands. These polymorphisms were screened against RILs in each population and associations were determined using one-way ANOVAs and Mapmaker. Yield data used for determination of associations was collected over five years in MI and Mexico where both stress and non stress treatments were applied.
Incorporation of the dominant gene Are, of Middle American origin, into commercial cultivars of Phaseolus vulgaris L., has been the main disease control strategy of plant breeders to limit the potential damage of Colletotrichum lindemuthianum (Sacc. & Magnus.) Lams.-Scrib. A random amplified polymorphic DNA (RAPD) marker designated OQ41440, generated by a 5′-AGTGCGCTGA-3′ decamer primer, was found tightly linked in coupling with the Are gene. OQ41440 mapped at 2.0 ± 1.4 centimorgans (cM) from the Are allele in the Andean genetic background and at 5.5 ± 2.3 CM in the Middle American background. A second coupling phase RAPD marker B3551000, generated by the 5′-GTATGGGGCT 3′ primer mapped at 5.4 ± 2.3 cM from the Are allele in the Andean genetic background and at 7.7 ± 2.7 CM in the Middle American background. Based on a recombination distance of 7.0 ± 1.9 cM between the two markers, OQ41440 and B3551000 RAPDs appear to flank the Are gene. The bracketing molecular markers allowed tagging of the Are allele with a selection fidelity of 99%. Use of the OQ41440 and B3551000 RAPD markers for marker-based selection will afford the opportunity to retain the Are anthracnose resistance gene in bean germplasm, as other epistatic resistance genes are characterized, and incorporated into contemporary bean cultivars.
Common bacterial blight (CBB), incited by the bacterial pathogen Xanthomonas axonopodis pv. phaseoli (Smith) Vauterin et al., is one of the most serious seed-borne diseases of common bean (Phaseolus vulgaris L.) worldwide. Although previous attempts to breed CBB-resistant bean cultivars have had limited success due to the quantitative nature of resistance, progress in marker-assisted selection has created new opportunities for breeders to improve the selection process. The potential of independent linked markers for indirect selection of CBB resistance was evaluated in field experiments in East Lansing and Saginaw, Mich. The presence of the SU91 marker was correlated with lower CBB leaf scores in East Lansing (r = −0.50***) and Saginaw (r = −0.59***) and correlated with pod resistance in Saginaw (r = −0.48***). SU91 exhibited a slight negative correlation with yield (r = −0.20*) in East Lansing but showed no association with yield in Saginaw. Plant selections carrying SU91 were crossed with a different source of CBB resistance linked to the sequence-characterized amplified region marker BC420 on bean linkage group B6. The effects of SU91 and BC420 markers were examined in two greenhouse studies. The presence of SU91 was correlated with lower CBB disease ratings for leaves (r = −0.20*) and pods (r = −0.27***). Presence of BC420 was only correlated with low pod ratings (r = −0.19*) in one experiment and CBB leaf resistance (r = −0.18*) in the second experiment. Presence of both markers resulted in lower levels of CBB resistance than provided by either marker alone, possibly indicating epistatic interactions between the independent loci conditioning CBB resistance in common bean.
Poinsettia (Euphorbia pulcherrima Willd. Ex Klotzch) `Freedom Red' (FR), `Success Red' (SR), and `Winter Rose Dark Red' (WRDR) and pansy (Viola wittrockiana Gams.) `Colossus Yellow Blotch' (CYB), `Delta Pure Yellow' (DPY), and `Majestic Giants Purple' (MGP) were treated with 14 different tank mix combinations of daminozide and chlormequat ranging from 0 to 4500 mg·L-1 daminozide and 0 to 1500 mg·L-1 chlormequat. The tank mix treatments reduced stem elongation for all three poinsettia cultivars. Total bract area of FR and canopy bract diameter of WRDR decreased linearly as daminozide or chlormequat concentration increased, while bract area of SR was affected by daminozide alone. Anthesis was not delayed by any of the plant growth regulator (PGR) applications. For pansies, growth responses to the PGR treatments varied with cultivar. CYB growth was affected by daminozide alone, DPY growth was affected by daminozide and/or chlormequat, while MGP growth was relatively insensitive to both PGRs. Time to flower of pansy was not affected by the PGR applications. Chemical names used: 2-chloroethyl N,N,N-trimethylammonium chloride (chlormequat chloride); butanedioic acid mono (2,2-dimethylhydrazide) (daminozide).
Ninety-eight percent of the navy beans (Phaseolus vulgaris) grown in the US are processed. Thus, new cultivars considered for release must meet industry standards. Canning quality behaves as a classical QTL which precludes its selection and evaluation in early generations. Such delays add a measure of inefficiency to a breeding program. Indirect selection for canning quality using molecular markers could increase efficiency. RAPD markers are more useful than RFLP's, in Phaseolus, due to a simpler protocol and a higher level of polymorphism within genetically related cultivars. Three populations of RIL's, derived from crosses between cultivars with standard and sub-standard canning quality, were screened to identify markers associated with canning quality. Material for evaluation was grown at two locations, in three replications and processed, in the Food Science Processing Lab, following industry standards. Quality traits measured were: processed texture, color and appearance. Associations of putative markers with canning quality were identified using ANOVA and Mapmaker programs