Stip: A Physiological Disorder of Pepper Fruits

Stip, a physiological disorder affecting bell and New Mexico (NM) pod type green chile pepper cultivars (both Capsicum annuum) has received limited formal academic attention. Symptoms present on fully developed fruits as black, brown, and yellow ovoid subcutaneous chlorotic lesions approximately 1.3 cm in length and 0.6 cm in width extending from the endocarp to the mesocarp without apparent expression in the cuticle. In this study, stip was characterized via microscopy and metabolomics assays, in addition to a greenhouse cultivar susceptibility experiment. Symptom development was induced in a greenhouse and the incidence, severity, and location of symptomatic pods was quantified for one reported resistant bell pepper cultivar, Cal Wonder 300, and one susceptible green chile pepper cultivar, AZ 1904, over two harvests. Fifteen potted plants of each cultivar were completely randomized on a greenhouse bench, and four temperature probes were deployed to monitor air and soil temperatures.  Greenhouse temperature set points of 14.4 °C and 28.9 °C (low and high, respectively) were used. Beginning in July, for a period of ten days, the temperature was allowed to reach 41.1 °C. At that time, symptoms of the disorder become apparent, pods were harvested, and stip incidence and severity were recorded. There was no statistically significant difference between the node location of symptomatic pods, incidence, or severity between the two cultivars indicating that the resistance reported in field studies may not be applicable to greenhouse conditions. More than 85% of symptomatic pods were located at or below the fifth node of the plant; of symptomatic plants, average stip incidence was 23%; and mean severity was four lesions per symptomatic pod. Under microscopic analysis, both cultivars presented identical fluorescent and confocal imagery; stip affected tissue was most apparent under green fluorescent protein and violet filters, which presented as a halo only around the lesions. These microscopy signals occurred only in close proximity to chlorotic lesions, and were not apparent in asymptomatic tissue from symptomatic pods, asymptomatic pods from symptomatic plants, nor asymptomatic tissue from asymptomatic plants. To gain additional insight into this disorder a polar and non-polar metabolite profile of green chile pods, and carotenoid analysis, was performed using tissue from susceptible cultivar AZ 1904 tissues collected from six different commercial fields in southern New Mexico in 2014. Sustained research emphasis is needed to fully understand the causes of this disorder, its effects on growers, and possible remedies.