No abstract

No abstract

European apple canker, caused by Neonectria ditissima, is a damaging disease of apple in many production regions worldwide. The pathogen infects apple trees through artificial or natural wounds. The most damaging phase of the disease is that cankers on main stems post-planting, most likely originating from infection in nurseries, can result in tree death in young orchards. Apple cultivars differ in their responses to the pathogen, which may be additionally affected by specific site factors. An experiment was conducted to study i) the susceptibility of seven cultivars to N. ditissima at three sites and ii) the effects of cold storage duration prior to planting on subsequent development of both main stem and peripheral cankers. Planting date had significant (albeit minimal effects) on the development of peripheral cankers only. Canker development differed greatly among the three sites and between the tested cultivars, with ‘Grenadier’ and ‘Golden Delicious’ being most resistant at all sites. The relative performance of cultivars in terms of canker development was generally consistent across the three sites. Nevertheless, the interaction between cultivar and site was still statistically significant for the development of main stem cankers, indicating that some site-specific factors may interact with cultivars to affect development of latent infections. Given the close proximity of the three sites (similar climatic conditions), the results indicate that further research is needed to investigate the effects of soil characteristics on canker development post-planting.

Rice (Oryza sativa) is an increasingly popular food in Africa. As much as 30% of yields are lost due to blast disease caused by Magnaporthe oryzae. Several commercial biopesticides of Bacillus subtilis, Trichoderma asperellum, and Serratia sp. strains were evaluated under field conditions for their effects against rice blast and yield at one site in Kenya and three sites in Tanzania in 2020 and 2021. Each biopesticide was applied as a dipping treatment at transplanting, post-transplanting foliar spraying, or both. Using biopesticides not only achieved blast control but also increased grain yield, particularly in low-production regions in Tanzania, with a yield increase of >100%. For higher-production sites with low disease pressure, the yield increase through biopesticides over the untreated control was limited, although significant disease suppression was achieved. Dipping alone was sufficient to suppress disease and improve yield unless disease pressure was high. The differences among the three biopesticides varied with site/year but generally were small. Improved yield using biopesticides is unlikely to result solely from reduced blast development, but also from improved plant development. The present study suggests that these commercial biopesticides should be applied in rice production, particularly in subsistence farming.

Aim We assessed the effect of exposing apple orchard soil to different temperatures and CO2 levels on the resident microbiome of soils from a conventionally managed and an organically managed apple orchard. The key difference between these two orchards was that synthetic fertilizers and pesticides are routinely used in the former one. Methods and results To investigate the effect of CO2 and temperature soil samples from each site at two depths were exposed to elevated temperature (29°C) at either 5,000 or 10,000 ppm for 5 weeks or control conditions (25°C + 400 ppm). Both bacterial and fungal communities were profiled with amplicon-sequencing. The differences between the two orchards were the most significant factor affecting bacterial and fungal communities contributing to 53.7% and 14.0% of variance in Bray-Curtis β diversity respectively. Elevated CO2 concentration and increased temperature affected organic orchard microbial diversity more than the conventionally managed orchard. A number of candidate beneficial and pathogenic microorganisms had differential abundance when temperature and CO2 were elevated, but their effect on the plant is unclear. Conclusions This study has highlighted that microbial communities in bulk soils are most significantly influenced by crop management practice compared to the climate conditions used in the study. The studied climate conditions had a more limited effect on microbial communitiy diversity in conventionally managed soil samples than in organically managed soils.