ROLE OF FUNGI VECTORED BY RICE STINK BUG (HETEROPTERA, PENTATOMIDAE) IN DISCOLORATION OF RICE KERNELS

Fungi, yeast, and bacteria were cultured from field-collected, discolored (pecky) rice, Oryza sativa L., kernels and from stylets and saliva of the rice stink bug, Oebalus pugnax (F.). A sterilized chrome wire was used to wound and introduce selected inocula into developing kernels on rice panicles. Typical kernel discolorations could not be induced by inoculation with bacterial or yeast isolates. When the caryopsis was wounded during inoculation, several fungi caused discoloration comparable to that of pecky kernels collected from rice fields. Fusarium oxysporum Schlect. caused the greatest discoloration followed by Cochliobolus miyabeanus (Ito & Kuribayashi) Drechsler ex Dastur, Curvularia lunata (Wakker) Boedijn, Alternaria alternata (Fr.) Keissler, and A. padwickii (Ganguly) M. B. Ellis. Symptoms typifying classical fungal discoloration peaked 5 to 10 d after anthesis, and classical insect damage symptoms peaked 15 d after anthesis when rice stink bugs were caged on plants 0, 5, 10, or 15 d after anthesis. In field tests, density of rice stink bug infestations was associated positively with incidence of discolorations historically attributed to insects and fungi. These data indicate that discolorations in pecky rice result from fungi being introduced at the time of feeding of O. pugnax by means of a loose vector relationship.