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H.M. Ariyarathne, D.P. Coyne, A.K. Vidaver, and K. Eskridge

The inheritance and heritability (H) of leaf and pods reactions and seed infection of common beans (Phaseolus vulgaris L.) to Xanthomonas campestris pv. phaseoli (Smith) Dye (Xcp) were studied in three crosses along with flower and stem color, and the association of reactions to Xcp in the plant organs. Recombinant inbred lines from the crosses `PC 50' × XAN 159, BAC 6 × HT 7719, and BelNeb 1 × A 55 were used. Quantitative inheritance patterns were observed for disease reactions in leaves, pods, and seeds. Stem and flower color were inherited qualitatively. Low to intermediate and intermediate H estimates were found for pod reactions when inoculated on the same time, allowing the infection to occur in a uniform environment. Intermediate to high H estimates were found for leaf and seed reactions to Xcp, respectively. Significant positive intermediate to moderately high correlations were found between the reactions to Xcp of the first trifoliolate with later-developed leaves and pods in all three populations. The moderately high genetic correlations between leaves and pods suggested that some common genes may control the reactions to Xcp in these plant organs. No association was detected between flower or stem color and reactions to Xcp.

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M.M. Welsh and K.F. Grafton

1 To whom reprint requests should be addressed. E-mail address: mmwelsh@wsu.edu We thank P.N. Miklas for providing the CBB-resistant seed. J.R. Venette provided Xanthomonas campestris pv . phaseoli strain F19

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E. Arnaud-Santana, M.T. Mmbaga, D.P. Coyne, and J.R. Steadman

We studied leaf and pod reactions of 18 Phaseolus vulgaris germplasm lines (three temperate and 15 tropical) to four Xanthomonas campestris pv. phaseoli (XCP) (Smith) Dye strains and seven Uromyces appendiculatus (UA) (Pers.) Unger races. Line × XCP interaction was significant for leaf and pod reactions. The common bean lines XAN-159, BAC-6, and XAN-112 had the best combined leaf and pod resistance to XCP. Line × UA race interactions were significant (P = 0.05). Lines IAPAR-14 and BAC-6 had the best combined resistance to XCP and UA.

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Mohamed F. Mohamed, Dermot P. Coyne, and Paul E. Read

The leaf reaction of the Phaseolus vulgaris L. germplasm—UNECA (M6 mutant derived from the cultivar Chimbolito, Costa Rica), `Chimbolito', BAC-6 (Brazil), XAN-159 (Centro Internacional de Agricultura Tropical, Cali, Colombia), and `PC-50' (Domican Republic)—to Xanthomonas campestris pv. phaseoli strain V4S1 (Dominican Republic) were determined in two replicated trials conducted in a greenhouse in Lincoln, Neb. (Feb.–Mar. and July–Aug. 1993). `PC-50' and `Chimbolito' were susceptible to Xcp strain V4S1 in both tests. UNECA, BAC-6, and XAN-159 had similar levels of resistance to Xcp in the July to August trial. However, in the February to March trial, the resistance of UNECA was greater than that of BAC-6 but less than that of XAN-159.

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Carlos A. Urrea, Phillip N. Miklas, and James S. Beaver

High levels of resistance to common bacterial blight caused by Xanthomonas campestris pv. phaseoli (Smith) Dye (Xcp) have been observed for tepary bean (Phaseolus acutifolius A. Gray var. latifolius Freeman). However, the inheritance of resistance from this source is unknown for many lines. The inheritance of common bacterial blight resistance was studied in four tepary bean lines crossed with the susceptible tepary bean MEX-114. Progenies were inoculated with a single Xcp strain 484a. Segregation ratios in the F2 generation suggested that resistance in Neb-T-6-s and PI 321637-s was governed by one dominant gene, and Neb T-8a-s had two dominant genes with complementary effects. These hypotheses for inheritance of resistance were supported by various combinations of F1, F3, BC1Pn segregation data in all lines except PI 321637-s where an additional minor-effect gene with recessive inheritance was indicated. Generation means analyses corroborated that multiple resistance genes were present in PI 321638-s. Lack of segregation for susceptibility among testcrosses for allelism between Neb-T-6-s/PI 321637-s, Neb-T-6-s/Neb-T-8a-s, PI 321637-s/Neb-T-8a-s, and PI 321637-s/PI 321638-s, suggested that one or more loci conditioning resistance to common bacterial blight were in common across the four tepary lines.

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M.E. Scott and T.E. Michaels

Effective genetic resistance to common bacterial blight [Xanthomonas campestris pv. phaseoli (Smith) Dye] is not present in common bean (Phaseolus vulgaris L.) cultivars grown in Ontario. Foliar symptoms and seed yield of white pea bean breeding lines from a P. vulgaris/P. acutifolius interspecific cross in the presence and absence of common blight were evaluated. In inoculated plots, seven of the 20 breeding lines did not differ significantly in severity of foliar symptoms from the most resistant controls, XAN 159 and XAN 161. The most susceptible lines tended to have the highest yield when grown under disease-free conditions (r = 0.61 and 0.49 at two locations). However, the susceptible lines showed an average yield loss of 25% when disease-free and inoculated plots were compared, while resistant lines had little or no yield loss. The most severely infected lines tended to have the greatest loss in yield (r = 0.72 and 0.53 at two locations). A resistant breeding line from this study is available as OAC 88-1.

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H.M. Ariyarathne, D.P. Coyne, A.K. Vidaver, and K.M. Eskridge

Breeding for resistance is an important strategy to manage common bacterial blight disease caused by Xanthomonas campestris pv. phaseoli (E. Smith) Dye (Xep) in common bean (Phaseolus vulgaris L.). It is necessary to determine if prior inoculation of the first trifoliolate leaf with Xcp influences subsequent reactions in other plant organs by increasing or decreasing resistance to Xcp. It is difficult to get an accurate estimate of heritability of disease reaction in pods since environment greatly affects the heritability estimate if flowering occurs over extended time periods. Thus, the disease reaction in attached pods versus detached pods was compared. A split-split plot design with two replications (growth chambers as blocks) was used, with bean lines as the whole-plot factors, Xcp strains as subplot factors, and bacterial inoculation treatments for leaf reactions or pod treatments as split-split plot factors. The first trifoliolate leaves, later developed leaves, and attached and detached pods were inoculated. No effects of prior inoculation on the disease reactions of subsequently inoculated leaves and pods were observed, indicating that the different plant organs can be inoculated at different times. The fact that detached and attached pods showed similar disease symptoms would suggest use of the former to reduce environment variance and improve heritability estimates of resistance.

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H.Z. Zaiter, D.P. Coyne, and J.R. Steadman

Ten dry bean (Phaseolus vulgaris L.) cultivars/lines with differential reactions to rust were used in growth chamber experiments to determine rust [Uromyces appendiculatus (Pers.) Unger var. appendiculutus, (U a)], and common bacterial blight Xanthomonas campestris pv. phaseoli (E.F. Sm.) Dews. (X c p)] reactions on leaves when coinoculated with both pathogens. The X c p-U a necrosis symptoms were very different from those caused by X c p alone. Depending on the level of host susceptibility to rust, the X c p reaction remained confined within the rust pustule or spread beyond the pustule area, causing a necrosis of the entire leaf. Prior infection of bean seedlings with bean common mosaic virus (BCMV), NY-15 strain, reduced rust pustule size, but did not affect the reaction to X c p. Screening with X c p and BCMV can be done at the same time during the early vegetative stage, but the interactions of U a with X c p and of BCMV with U a need to be considered in screening for resistance.

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Mohamed F. Mohamed and Dermot P. Coyne

Common bacterial blight, incited by Xanthomonas campestris pv. phaseoli (Smith) Dye (Xcp), is a serious disease of common beans (Phaseolus vulgaris L.). Three experiments were conducted twice in growth chambers at 26 ± 1C under short (10 hours light/14 hours dark) and long (16 hours light/8 hours dark) photoperiods to determine the influence of these photoperiods, flower bud removal, pod development, and pre- and post-inoculation photoperiods on the reaction of common beans to Xcp. In one test, `PC-50' (susceptible; S) flowered earlier and was more susceptible to Xcp under the short photoperiod than under the long photoperiod. BAC-6 (resistant; R) flowered at the same time under both photoperiods but developed rapid leaf chlorosis (RLC) (hypersensitive reaction) under long photoperiods. Flowering and disease reactions to Xcp by XAN-159 (R) were similar under both photoperiods. In a second test, daily removal of flower buds of `PC-50' decreased its susceptibility to Xcp under the short photoperiod. RLC of inoculated leaves of BAC-6 occurred during flowering and pod development under both photoperiods. XAN-159 expressed a high level of resistance to Xcp but showed RLC at later pod development stages. In a third test, the disease reaction of `PC-50' was affected by the particular photoperiod applied post-inoculation but was not influenced by the photoperiod applied before inoculation with Xcp. The implications of these results in breeding beans for resistance to Xcp are discussed.

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Soon O. Park, Dermot P. Coyne, Nedim Mutlu, Geunhwa Jung, and James R. Steadman

Common bacterial blight, incited by Xanthomonas campestris pv. phaseoli (Xcp) is a serious disease of common bean (Phaseolus vulgaris L.). Randomly amplified polymorphic DNA (RAPD) markers and flower color (V gene) previously were reported to be associated with six quantitative trait loci (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. The 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 recombinant inbred (RI) backcross population from the cross BC2F6 `PC-50' × XAN-159 and for leaf resistance to Xcp in an F2 population from a different cross pinto `Chase' × XAN-159 could be confirmed. One or two genes from XAN-159 controlled leaf and pod resistance to Xcp. 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. One to three QTL affecting leaf and pod resistance to Xcp accounted for 22% to 61% of the phenotypic variation. Gene number (one to two) estimations and number of QTL (one to three) detected for leaf and pod resistance to Xcp in the RI backcross population were generally in agreement. The marker BC437.1050 and V gene, along with other resistance genes from other germplasm, could be utilized to pyramid the different genes into a susceptible or partially resistant bean line or cultivar to enhance the level of resistance to Xcp.