Pseudomonas syringae pv. syringae (bacterial canker or blast (stone and pome fruits)).

P. syringae pv. syringae occurs in many areas, from the tropics to the frigid zone (e.g. Alaska). It attacks major crops, including beans (Phaseolus vulgaris), cowpeas, stone fruits, pome fruits, kiwi fruit and grain sorghum. The diseases caused by this bacterium are very important in many countries throughout the world. For instance, bacterial brown spot occurs wherever beans are grown, and canker diseases of fruit trees caused by P. syringae pv. syringae are widespread and may be devastating, causing great losses or requiring much effort to protect plants from them.

Grain yield, stability and bacterial brown spot disease of dark red kidney dry bean (Phaseolus vulgaris L.) genotypes across six environments in South Africa

Dry bean (Phaseolus vulgaris L.) is grown under an extensive range of agro-climatic conditions and is an essential source of protein and income globally. This study aimed to evaluate yield performance, stability, and bacterial brown spot (BBS) disease resistance of fourteen dark red kidney genotypes across environments in South Africa namely Carolina, Clarens, Cedara, Middelburg, Potchefstroom, and Warden. Analysis of variance (ANOVA), additive main effects and multiplicative interaction (AMMI) and the genotype plus genotype by environment interaction (GGE-biplot) analysis were used to evaluate grain yield performance, stability, and BBS disease resistance. The AMMI ANOVA revealed that mean squares for grain yield and BBS severity for the environment, genotype, and genotype by environment interaction were highly significant (P<0.001). Four interaction principal components (IPCA1 - 4) for grain yield and IPCA1 for BBS severity were highly significant (P<0.001, P<0.01). Genotype G12 showed broad adaptation for both high grain yield and low BBS severity across the six environments, while genotypes G08, G06, G03, G02, G05, and G04 had specific adaption for high grain yield and low BBS severity. These genotypes recorded grain yield above the grand mean and the best check cultivar, both with 1.43 t ha-1 , and BBS severity below the grand mean (31.90%) and the best check (48.89%). The genotypes identified with either broad or specific adaptation can be released in the environments they are adapted to, or used as parents in breeding programmes aiming to improve grain yield and BBS disease resistance of dry bean for farmers in South Africa.

Screening Andean Diversity Panel Dry Bean Lines for Resistance to Bacterial Brown Spot Disease Under Field Conditions in South Africa

Bacterial brown spot (BBS) disease caused by Pseudomonas syringae pv. syringae is an important disease of dry bean (Phaseolus vulgaris L.), with grain yield losses of 55% reported in South Africa. This study aimed to identify BBS disease-resistant genotypes from 415 Andean Diversity Panel (ADP) dry bean lines and 5 check cultivars under field conditions across three sites in South Africa: Warden and Middelburg under natural infestation and Potchefstroom under artificial inoculation. Plants at Potchefstroom were inoculated with P. syringae pv. syringae using three isolates at 21, 28, and 36 days after planting, and disease scoring was done at 7, 14, and 21 days after inoculation following a modified 1 to 9 International Centre for Tropical Agriculture (CIAT) scale. The BBS severity percentage and the area under the disease progress curve (AUDPC) were applied to quantify the reaction of bean genotypes to BBS disease. The study identified 17.2% of evaluated germplasm as resistant and 45.3% as moderately resistant. Genotypes ADP-0592, ADP-0790, ADP-0120, and ADP-0008 were selected for both resistance and high seed yield across the three environments. Genotypes ADP-0546, ADP-0630, ADP-0120, and ADP-0279 were selected for both high yield and resistance at Warden, whereas ADP-0038, ADP-0721, and ADP-0790 were selected for both traits at Middelburg, and lastly, ADP-0120 and ADP-0079 were selected for both traits at Potchefstroom. The best genotypes selected for both high yield and BBS resistance had grain yield >1.45 t ha−1 across sites and >1.85 t ha−1 at individual sites, and they out yielded the best-performing check cultivar (1.13 t ha−1) and the grand mean yield (0.87 t ha−1) across sites. The AUDPC had a strong negative correlation (r = −0.55, P < 0.001) with grain yield at Potchefstroom. Medium-seeded genotypes showed a lower AUDPC than the large-seeded genotypes, and indeterminate genotypes showed a lower AUDPC than determinate genotypes. The genotypes selected for resistance and yield can be utilized in future dry bean improvement efforts for the South African bean market.