Dynamics of ascospore production in late autumn to develop better apple scab management strategies

通常认为，苹果赤霉菌的有性繁殖的年度周期发生在冬季的落叶上，产生子囊孢子作为第二年春天的主要接种物。此外，还假定不同交配类型的赤霉菌株系之间的随机交配。然而，我们最近发现，过去十年在混合果园中收集的数据并不支持这种随机交配假设。我们的数据表明，来自同一叶片上病斑的分离物之间的有性交配更有可能发生和成功，而不是果园地上落叶层中独立感染的叶片之间的接触。此外，我们的结果还表明，有性生殖很可能在落叶之前就开始了。如果这些是真的，我们需要重新审视当前关于赤霉病种群遗传学的共识/假设，特别是关于现有真菌毒力因子的重组、使用混合果园的可行性以及减少落叶前有性繁殖的管理措施。这项建议将获得直接证据，以回答是否在落叶之前开始性行为；是否在同一叶子上的病斑之间更有可能成功性行为。然后，我们将开发和评估(主要是基于微生物的方法)控制措施，以扰乱有性繁殖。最后，我们将在NIAB EMR上使用赤霉病指示基因的独特集合(作为全球赤霉病毒力监测计划的一部分)来证明不太可能重组赤霉病毒力因子。研究结果将对抗病基因的耐久性预测、混合果园应用的可行性、减少一次接种量等方面产生重大影响。

It is commonly assumed that the annual cycle of sexual reproduction of the apple scab fungus takes place on fallen leaves in the winter, producing ascospores as primary inoculum for the next spring. Furthermore, random mating among scab strains of opposite mating types is assumed. However, we recently showed that this random mating assumption is not supported by the data collected in a mixed orchard over the last ten years. Our data suggested that sexual mating is more likely to take place and succeed between isolates from lesions on the same leaf than contact between independently infected leaves in leaf litter on the orchard floor. Furthermore, our results also suggest that sexual reproduction is likely to be initiated before leaf-fall. If these are true, we need to re-visit current consensus/assumptions of scab population genetics, particularly regarding the recombination of existing fungal virulence factors, practicality of using mixed orchards, and management measures to reduce sexual reproduction before leaf-fall. This proposal will obtain direct evidence to answer Whether sex is initiated before leaf-fall;whether sex is more likely to succeed between lesions on the same leaves.Then, we will develop and evaluate (mostly microbial-based methods) control measures to disrupt sexual reproduction. Finally, we shall use the unique collection of scab indicator genotypes (as part of the global scab virulence monitoring programme) at NIAB EMR to demonstrate that recombination of scab virulence factors is unlikely. The results will have huge impact on predicting durability of resistance genes, feasibility of using mixed orchards, and reducing primary inoculum.