Genotype x environment interactions for resistance to common scab in tetraploid potato

Common scab of potato (Solanum tuberosum L.), caused by the soil-borne bacterium Streptomyces scabies (Thaxter) Lambert & Loria, is an economically important potato disease. Tubers from susceptible plants may have superficial, raised, or pitted lesions. Quantitative methods to evaluate tubers for the amount of surface area covered (Al) and the type of lesion (LI) have previously been developed. The purposes of this study were to (i) estimate broad-sense heritability on a mean basis for scab resistance in a tetraploid population of Solanum tuberosum for AI and LI, (ii) determine the importance of genotype x environment interactions on AI and LI, and (iii) determine the stability of potato genotypes for scab resistance. In 1992 and 1993, 23 potato clones were grown in replicated scab-infested field plots in Presque Isle, ME, and Cranesville, WV, and rated for AI and LI, There were significant environment, genotype, and genotype x environment effects for AI and LI. Broad-sense heritabilities on a mean basis and their exact 95% confidence intervals for Al and LI were estimated as 0.89 (0.78, 0.95) and 0.93 (0.86, 0.97), respectively. Shukla's stability-variance statistics indicated that the most scab resistant genotypes were the most unstable, whereas, the most susceptible genotypes were the most stable, Thus, disease pressure was intense. Moderate levels of scab resistance were found. However, to obtain genotypes with high levels of scab resistance that are stable across environments will probably require development of populations incorporating new sources of scab resistant germplasm.