Cyclic production of sporangia and zoospores by Phytophthora capsici on pepper roots in hydroponic culture

Abstract

Production of sporangia and zoospores by Phytophthora capsici on roots of hydroponically grown peppers was shown to be cyclic in nature. Production of sporangia on peppers grown with a 12 h light : 12 h dark photoperiod was mainly diurnal: percentage of full sporangia began to increase between hours 8 and 10 of the dark cycle, the greatest number of full sporangia was present at hours 10–12 of the light cycle, and empty sporangia were most abundant at hours 4–8 of the dark cycle. Zoospore production was primarily nocturnal; populations began to increase at the start of the dark cycle and, in general, peaked sharply at hour 4. Altogether, 79.5% of the zoospores, sampled every 2 h over a 24 h period, were isolated from the hydroponic solution during the dark cycle. Extending the light cycle by 2 h delayed the peak in zoospore production by 2 h, so that it still occurred at hour 4 of the dark cycle. When peppers were grown under continuous light, no cyclic pattern of sporangia and zoospore production occurred. These findings could enhance the success of detection methods and practices for managing zoosporic pathogens in recycled irrigation water.