Temperature and genotype shape the protective effect of a Bacillus-based biocontrol product against Alternaria leaf blight in carrot

Résumé fourni par la source

Bacillus -based plant protection products (bioPPPs) can suppress foliar diseases through direct antifungal activity and activation of plant defence responses. However, their efficacy can vary with temperature and host genotype, and the mechanisms underlying this variability are poorly understood. We investigated whether a prolonged high-temperature period alters the efficacy of a Bacillus pumilus -based bioPPP and the associated pathogen- and plant-related responses against Alternaria leaf blight caused by Alternaria dauci in carrot. Two carrot genotypes with contrasting basal resistance, Bolero and Presto were sprayed with the bioPPP or water and inoculated 48-h later under normal temperature (NT; 23 °C) or high temperature (HT; 34–45 °C). Disease development was summarised as AUDPC. Conidial germination and hyphal development were quantified in vitro , and pre-inoculation defence gene expression was profiled by RT-qPCR. Under NT, the bioPPP significantly reduced disease severity in both genotypes. Under HT, however, protection was genotype-dependent. In vitro assays showed that both HT and the bioPPP constrained early conidial germination, whereas post-germination hyphal expansion was largely limited by HT. Pre-inoculation transcriptional profiling showed that the bioPPP was associated with increased expression of selected defence-related gene involved in PR proteins, oxidative processes and cell-wall remodelling in Bolero under NT, but this response was attenuated under HT. Presto displayed a weaker but temperature-reprogrammed defence profile. Together, these results indicate that Bacillus -based protection is associated with both direct antifungal pressure and genotype- and temperature-dependent changes in host defence status, although the causal contribution of these defence responses remains to be functionally validated.

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