Screening for Resistance to Bacterial Fruit Blotch in Watermelon Fruit.

A screening study was undertaken on 1480 watermelon PIs and cultigens to determine fruit resistance to Acidovorax citrulli, the causal agent of bacterial fruit blotch, under field conditions. Various inoculation methods were evaluated over three years to determine the optimal method (timing, inoculation method, and concentration). Inoculation at anthesis frequently led to rapid fruit senescence, bagging fruit to increase humidity also often led to fruit senescence, and a wide range spray inoculum concentrations produced similar disease severities. The watermelon collection was screened for three years (2015-2017) in 9 reps, and resistant lines were extensively retested in 2016 and 2017. The watermelons were spray-inoculated with group I and group II isolates 1-2 weeks post-anthesis and rated for disease severity after three weeks. Forty-two PIs were found to be highly resistant, though no lines were completely symptom-free in all replications. The most resistant 15 PIs (13 Citrullus lanatus, 1 Citrullus mucosospermus, and 1 Citrullus amarus) were selfed and the progeny were tested in 2017 to confirm resistance and create lines for further research.