Optimization of N fertilizer and synergistic intercropping to enhance the productivity advantage of faba bean and effective control of chocolate spot epidemics.

Intercropping of wheat/faba bean is a common practice within the legume-cereal family. However, the benefits of nitrogen (N) fertilizer optimized synergistic intercropping in improving faba bean productivity while controlling the prevalence of chocolate spot disease have not been established. This study conducted continuous field experiments spanning two planting seasons to investigate two key findings. (1) Optimizing N fertilizer application can enhance the productivity of intercropped faba bean. (2) The percentage severity index (PSI) during the period of maximum prevalence rate (Rmax) of faba bean chocolate spot disease, poses a substantial challenge to faba bean yield. The results indicated that the land equivalent ratio and transgressive overyielding index for each intercropping treatment increased with higher N fertilizer application, exceeding a value of 1, and the land saving proportion also exceeded 0. Intercropping primarily enhances productivity, as measured by the harvest index (HI), by amplifying the complementary effect rather than the selection effect, thus improving the net benefit of intercropping. The HI of single and intercropped faba bean increased with the N1 and N2 treatments in both planting seasons. However, the HI of single and intercropped faba bean at the N3 level decreased significantly, ranging from 17.85% to 29.62%. Furthermore, a notable negative correlation was established between the PSI during critical epidemic (initial epidemic, maximum epidemic rate, and late epidemic) periods and observed and expected faba bean yields. As PSI increased, faba bean yields decreased and PSI of intercropping at different periods were lower than those observed in the single cropping. Additionally, intercropping with the optimized N fertilizer treatment (N2 treatment) exhibited an enhanced relative control effect on chocolate spot disease in faba bean, ranging from 35.21% to 52.36%. This finding confirmed the productivity advantage of intercropping faba bean. In conclusion, this study suggested that optimizing N fertilizer application can enhance the productivity of intercropped faba bean. Wheat/faba bean intercropping effectively controlled the PSI during the period of Rmax, which would otherwise threaten faba bean yield. Consequently, this practice ensured sustained advantages of wheat/faba bean intercropping.

The severity and yield effects of the chocolate spot disease in faba bean affected by intercropping and nitrogen input.

BACKGROUND: The aim is to study the disease suppression efficiency, yield loss rate, and yield benefits of intercropped faba bean against chocolate spot under nitrogen (N) input, to clarify the effectiveness of intercropping faba beans in controlling chocolate spot and its contribution to yield increase. RESULTS: Four N input levels and disease suppression treatments were discovered when faba bean-wheat intercropped was used. Adding N enhanced the chocolate spot's area under disease progression curve (AUDPC) by 27.1-69.9%. In contrast to monoculture, intercropping reduced the AUDPC of the chocolate spot by 32.4-51.0% (P < 0.05). Interestingly, the relative control efficacy (RCE) of intercropping at the EShan site was better. With disease suppression or non-suppression, N input increased grain yield loss and its components in faba bean. The total yield advantage effect (TE) and disease-suppression effect (DSE) of faba bean intercropped at the two experimental sites were significantly increased under N input (N1 and N2 level). The proportion of recovery yield due to intercropping suppressed disease (DSE/TE ratio) in EShan (52.1%) was higher than that in Xundian (40.9%), and the DSE of intercropping played an indispensable role in the two sites. Regression analysis of AUDPC and grain yield loss amount showed that one unit increase in chocolate spot AUDPC could cause a grain yield loss of 0.38-0.86 kg ha-1 . The partial land equivalent ratio (pLER) of intercropping faba beans at the EShan site was > 0.33. CONCLUSION: In conclusion, intercropped faba bean with N treatment (45-90 kg ha-1 ) was the best choice for maximizing the intercropping disease control effect. © 2023 Society of Chemical Industry.

Identification of Faba bean genetic loci associated with quantitative resistance to the fungus Botrytis fabae, causal agent of chocolate spot.

Introduction: Chocolate spot, caused by the ascomycete fungus Botrytis fabae, is a devastating foliar disease and a major constraint on the quality and yield of faba beans (Vicia faba). The use of fungicides is the primary strategy for controlling the disease. However, high levels of partial genetic resistance have been identified and can be exploited to mitigate the disease. Methods: The partially resistant V. faba cultivar Maris Bead and susceptible Egyptian accession ig70726 were crossed, and a genetic mapping population of 184 individuals was genotyped in the F2 generation and screened for resistance to B. fabae infection in the F3, F5, and F6 generations in a series of field experiments. A high-density linkage map of V. faba containing 3897 DArT markers spanning 1713.7 cM was constructed. Results: Multiple candidate quantitative trait loci (QTLs) in 11 separate regions of the V. faba genome were identified; some on chromosomes 2, 3, and 6 overlapped with loci previously linked to resistance to Ascochyta leaf and pod blight caused by the necrotrophic fungus Ascochyta fabae. A transcriptomics experiment was conducted at 18 h post-inoculation in seedlings of both parents of the mapping population, identifying several differentially expressed transcripts potentially involved in early stage defence against B. fabae, including cell-wall associated protein kinases, NLR genes, and genes involved in metabolism and response to reactive oxygen species. Discussion: This study identified several novel candidate QTLs in the V. faba genome that contribute to partial resistance to chocolate spot, but differences between growing seasons highlighted the importance of multi-year phenotyping experiments when searching for candidate QTLs for partial resistance.

Assessing agronomic performance, chocolate spot resistance, and heat tolerance for diverse Vicia faba genotypes under varying environmental conditions.

Chocolate spot and heat stress devastatingly impact the production of faba bean, particularly under prevailing climatic changes and rising drastic environmental conditions. Hence, the adaptability of faba bean performance is a decisive objective of plant breeders to ensure its sustainable production. The present study aimed to evaluate the agronomic performance and stability of diverse eleven faba bean genotypes for yield characters, chocolate spot, and heat stress in eight different growing environments. The faba bean genotypes were evaluated at two sowing dates in two different locations during two growing seasons. The evaluated eleven faba bean genotypes were sown timely in autumn (25 October) and late sowing in early winter (25 November) in Bilbeis and Elkhatara during 2020 and 2021 growing seasons. The results exhibited substantial differences among the evaluated sowing dates, locations, and faba bean genotypes for all studied characters. The genotypes Sakha-3, Nubaria-3, Nubaria-5, Misr-3, and Wadi-1 were able to produce acceptable yield and quality characters under timely sowing in autumn and late sowing in early winter in all tested environments. Moreover, the genotypes Nubaria-3, Nubaria-4, Nubaria-5, Sakha-4, Giza-3, and Triple White exhibited better resistance to chocolate spot. The assessed faba bean genotypes were evaluated under late sowing to expose the plants to high temperature stress at flowering and throughout the anthesis and seed-filling stages. The genotypes Nubaria-5, Nubaria-3, Nubaria-4, Sakha-3, Sakha-4, Wadi-1, and Misr-3 possessed tolerance to heat stress more than the other genotypes. Different statistical methods were applied to study the stability of assessed genotypes such as joint regression, Additive Main Effect and Multiplicative Interaction (AMMI) analysis, AMMI stability value, Wricke's and Ecovalence values. The estimated stability parameters were consistent in depicting the stability of the assessed faba bean genotypes. The findings revealed that Sakha-1, Misr-3, Nubaria-4, and Nubaria-5 demonstrated stable and desirable performance across all tested environments. The heatmap was employed to classify the assessed faba bean genotypes into different groups based on agronomic performance, chocolate spot resistance and heat stress tolerance. Nubaria-3, Nubaria-4, Nubaria-5, and Misr-3 had the best performance for agronomic performance, chocolate spot resistance, and heat stress tolerance. The obtained results provide evidence of employing promising faba bean genotypes for improving the stability of agronomic performance, chocolate spot resistance, and heat stress tolerance in breeding programs principally under unprecedented climate fluctuations.