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Expanded effector families in fruit scab fungi: Venturia inaequalis, V. pirina and V. nashicola

Kim Plummer: Plant Biosecurity CRC

<div><em>Venturia inaequalis</em>, <em>V. pirina and V. nashicola,</em> are host-specific fungi, causing scab disease on apples, European pears and Asian pears, respectively. Frequent fungicide applications are required for scab control, and fungicide resistance and residues are an on-going issue. Disease-resistant germplasm exists, however it is critical to aim for selection of durable disease resistance, as breeding is slow with these woody, outcrossing hosts. The genetics of host-cultivar resistance to the apple scab fungus follows the gene-for-gene model: pathogen effectors are secreted into the host environment during infection and a subset of these may be recognised as avirulence (Avr) determinants by cognate plant resistance (R) proteins to induce a resistance response. Few <em>R</em> genes, and no <em>Avr</em> genes have been cloned in scab pathosystems. Furthermore, the molecular basis of non-host resistance is unknown. Comparison of predicted secretomes of <em>Venturia spp. </em>revealed genus and species-specific effector candidates that may determine host range. Many orthologues of known fungal effectors were also identified; including<em> Ecp6</em>, <em>AvrLm6 </em>and<em> Ave1</em>. <em>AvrLm6</em> is represented by an expanded family of over 25 genes in individual <em>Venturia</em> genomes (<em>Leptosphaeria maculans</em> isolates have 2)<em>. </em><em>Ave1 </em>orthologues are represented by over 12 members in each <em>Venturia</em> genome. These, and other effector candidates, are currently being functionally characterized.</div>