PROTEASE INHIBITORS AND REPRODUCTION OF ROTYLENCHULUS RENIFORMIS IN PINEAPPLE

Protease inhibitors (PIs) are thought to serve as defense compounds against pathogen attack in many plant systems. PIs have been found in pineapple roots, and populations of Rotylenchulus reniformis remain untypically low for 6-9 months after pineapple planting. A greenhouse experiment was conducted to determine if PIs present in pineapple roots affected nematode reproduction. Pineapple plants with and without R. reniformis were harvested monthly and assayed for PI activity and nematode population densities. Pineapple PI activity increased for the first 6 months after planting (in both inoculated and non inoculated treatments), and was higher in nematode inoculated plants than non-inoculated plants (P<0.05). Nematode reproduction (egg numbers) was not correlated to PI activity. A second experiment was conducted to determine if PI levels in pineapple roots varied along root length in the presence and absence of nematodes. PI activity increased in the presence of nematodes and this increase was concentrated in the basal portion of the roots where nematode densities were highest. These results support a defensive role for PI in pineapple roots.