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COMPLETION OF TESTING OF Phaseolus coccineus PLANT INTRODUCTIONS (Pis) FOR WHITE MOLD, Sclerotinia sclerotiorum, RESISTANCE

Barbara Gilmore, James R. Myers, and Deborah Kean, Dept. of Horticulture, Oregon State Univ., Corvallis, OR 97331

White mold, causal pathogen Sclerotinia sclerotiorum (Lib.) de Bary, results in widespread yield and quality loss of snap and dry beans. In favorable white mold environments 100% of the crop may be lost. In the United States, the annual yield loss to white mold is about 3.5% for dry beans and 2% for snap beans. Furthermore, processing plants may reject snap bean lots if pod infection rate exceeds 2% [3]. Resistance in common bean has taken the form of temporal avoidance, architectural avoidance and physiological resistance mechanisms. Studies have shown that these forms of resistance are inherited quantitatively and have low heritabihty [3]. One test for physiological resistance of beans to white mold is the straw test developed by Petzoldt and Dickson [4]. P. coccineus is known to possess greater resistance to this disease than does P. vulgaris [1]. We used the straw test method to examine all available accessions of the P. coccineus collection held by the National Plant Germplasm System that we had not previously tested in 1999. The number of accessions tested in 2001 was 334, including 50 lines that had high levels of resistance in our 1999 test. We inoculated seedlings 23 to 25 days after planting, and read them 8 days later. Plants that appeared resistant at time of reading were re-inoculated after 13 to 15 days, and were read again 8 days later. The controls OR 91G, a susceptible snap bean, and MO 162, a fairly resistant dry bean, were inoculated at 31 days because extra time was needed to obtain sufficient growth for testing. On a scale of 1-9, a rating of 3 or less imphes a high degree of resistance while a score of 7 or greater indicates a high degree of susceptibility. A plant was scored as 4 when white mold mycelial growth stopped at the first node. Average white mold ratings for OR 91G and M0162 were 5.5 and 4.5, respectively. Overall average white mold scores for the three species in the P. coccineus collection were: P. coccineus = 4.01, P. polyanthus = 4.78 and P. vulgaris = 4.44. Table 1 shows the 40 most resistant accessions identified in our screen. The seeds of each accession were examined and separated by species and also by seed color. Seed color was used as a category because P. coccineus and P. polyanthus (previously P. coccineus spp. Darwinianus [2]) may have considerable out-crossing. Several accessions were a mix of two or three species. The average number of seeds tested per accession was 14. In our studies many plants that appeared resistant at the first straw test reading slowed, but did not stop the white mold's advance. To further characterize resistance, plants were observed, usually for about three more weeks, to see if the plant's defenses fully halted the mycelium's growth. If any plant in a pot allowed the mold to advance past the first node, the line received an asterisk (Table 1). Multiple asterisks were assigned when an accession had different species, color categories or multiple pots. References 1. Abawi, G.S., Prowidenti, R., Grossier, D.C. & Hunter, J.E. 1978. Inheritance of resistance to white mold disease in/*, coccineus. J. Hered. 69:200-202. 2. Debouck, D.G. 1999. Diversity in Phaseolus species in relation to common bean. p. 25-52. In: Singh, S.P. (ed.) Common Bean Improvement in the twenty-first Century. Kluwer, Dordrecht. 3. Lyons, M., Dickson, M. & Hunter, J. 1987. Recurrent Selection for Resistance to White Mold in Phaseolus Species. J. Amer. Soc. Hort. Sei. 112(1): 149-152. 4. Petzoldt, R. & Dickson, M. 1996. Straw Test for Resistance to White Mold in Beans. BIG 39: 142-143. 65

Table 1. Evaluation of white mold resistance of the Phaseolus coccineus collection' Seed color Pl# Origin Em^ Species No.seeds l^'testAV CM* 2"°testAV 165421 Gray Mexico H P. coc 14 3.4 4.0 193045 Black * Guatemala H p. coc 12 3.4 4.5 196413 Black Guatemala E p. vulg 14 4.1 5.0 201297 Color mixture* * Mexico H P. coc 13 3.6 3.7 201304 Color mixture* Mexico H P. coc 21 3.0 3.4 201320 Red * Mexico H P. coc 15 3.7 2.5 201366 Color mixture* Mexico H P. coc 13 3.8 3.4 209669 Color mixture* * Mexico H P. coc 11 3.5 3.9 311194 * Small Red" Guatemala E p. vulg 13 3.6 3.7 311217 Brick Red * Guatemala E P. poly 10 4.3 4.0 311819 Color mixture* Guatemala H P. coc 13 3.7 3.7 311859 Black Guatemala E P. vulg 15 3.7 4.3 311985 Dark Pink Mexico H P. coc 13 3.5 3.3 313310 Tan Mexico E P. poly 17 3.9 4.7 317551 Tan « Guatemala H P. coc 13 2.9 3.6 317575 Red Guatemala E P. poly 12 4.3 5.0 317576 * Color mixture* Guatemala E P. poly 16 4.4 4.0 325599 Color mixture* Mexico H P. coc 15 3.7 4.0 361371 * Mottled Tan Bhutan H P. coc 15 3.5 4.3 361510 * Color mixture* India H P. coc 11 3.6 4.2 433236 White Guatemala H P. coc 12 2.7 * 3.8 433237 Color mixture* Guatemala H P. coc 13 3.5 * 3.4 433242 Color mixture* Guatemala H p. coc 14 3.3 ** 3.3 433246 Pink Guatemala H P. coc 14 2.4 2.3 433247 ** Color mixture Guatemala H p. coc 13 3.5 3.0 433250 * Tan Guatemala H p. coc 13 3.7 2.8 433251 * Color mixture Guatemala H p. coc 12 3.3 3.6 439534 * Mottled Pink Netherlands H p. coc 14 3.1 3.4 451863 Color mixture* Guatemala H p. coc 12 3.0 4.1 451868 White Guatemala E p. vulg 14 3.6 * 4.3 451873 Pink" Guatemala E P. vulg 6 3.8 * 3.5 475745 White Netherlands H P. coc 13 3.0 3.8 583554 * White Japan H P. coc 12 3.1 3.9 311184 ** Red Guatemala E P. poly 14 3.9 3.6 189023 Color mixture Guatemala H P. coc 12 2.7 3.2 311210 Black" * Guatemala H P. coc 13 3.2 3.9 317550 ** Color mixture"* Guatemala E P. poly 14 4.1 3.7 407387 White" China H P. coc 10 3.9 3.8 433253 ** Color mixture Guatemala H P. coc 15 3.3 3.7 313417 Color mixture" Mexico H P. coc 22 3.1 4.0 ^Included are accessions classified as P. coccineus that contained P. polyanthus and P. vulgarís. ^Em = emergence, either hypogeal or epigeal. ^CM refers to continuation of the white mold down the stem of the plant after the initial eight day reading. ^Color mixture refers to accessions that had multiple seed colors, but all colors appeared to be about equal in their resistance rating. ''One species in a mixed accession that had greater resistance. ''Accessions that had been tested in 1999, and then were retested in 2001.