New insights into biology, transcriptome analysis and control strategies of the cucurbit pathogen Podosphaera xanthii

Podosphaera xanthii is the main causal agent of cucurbit powdery mildew (CPM) in southern Italy, where the disease management is difficult and requires numerous fungicide sprays per season. The effectiveness of several biological control agents (BCAs), botanicals (BOTs) and fungicides was evaluated in a field trial on Cucumis melo local ecotype ‘Barattiere’. Orange oil, sulphur, potassium bicarbonate and laminarine showed a good effectiveness and reduced the CPM severity on leaves as compared to the untreated control. Sexual reproduction increases genetic variation and can promote the differentiation of new more adapted genotypes. P. xanthii is a heterothallic fungus; both idiomorphs MAT1-1 and MAT1-2 were detected in more than half of 23 monitored sites and, according to the whole data, the MAT1-1 and MAT1-2 are in 1:1 ratio. The capability of six MAT1-1 and ten MAT1-2 isolates in yielding fertile crosses and differentiate chasmothecia was proved under laboratory conditions. Chasmothecia were also detected, although sporadically, in the field. RNA-Seq experiments (Illumina technology) were carried out using two isolates of opposite mating types and their cross to obtain a detailed de novo Trinity-based assembly of the transcriptome of P. xanthii. The 23,065 transcripts obtained were employed in: i) the analysis of differential expressed transcripts; ii) the identification of putative effectors, transposable elements (TEs) and mycoviruses; iii) the molecular characterization of the MAT1 locus in P. xanthii. The availability of new genomic and transcriptomic data will promote new insights on the population biology of the pathogen and CPM sustainable management.