CITRUS ROOTSTOCK RESPONSES TO HERBIVORY BY LARVAE OF THE SUGARCANE ROOTSTOCK BORER WEEVIL (DIAPREPES-ABBREVIATUS)

The responses of roots to feeding by larvae of a citrus root weevil (D iaprepes abbreviatus) were investigated in Citrus grandis (L. Osb. x P oncirus trifoliata (2N) (L.) Raf.; C. grandis x P. trifoliata (4N); P. trifoliata x C. glandis (Flying Dragon x Nakon); C. paradisi Macf. x P. trifoliata (Swingle citrumelo), C. aurantifolia (Christm.) Swingle (Citrus macrophylla); C. reticulota Blanco (Cleopatra mandarin); C. si nensis (L.) Osb. x P. trifoliata (Carrizo citrange); C. aurantium (L.) (sour orange). Chitinase, chitosanase, beta-1,3-glucanase, peroxidase and lysozyme activities were measured and significant differences wer e observed for some of the cultivars between infested and uninfested r ootstocks. Generally, increased activities were observed for chitinase s and decreased activities were observed for the other enzymes measure d. Numerous significant differences in hydrolase and peroxidase activi ties were observed between cultivars. Immunological detection revealed that new protein bands occurred in root protein extracts for six of t he eight cultivars infested with larvae when an antibody to a class I potato leaf chitinase was used. Antibodies generated against two citru s chitinases of M(r) 24 000 (basic chitinase cv. Valencia (C. sinensis ) callus, BCVC) and M(r) 28 000 (basic chitinase/lysozyme cv. Valencia callus, BCLVC) indicated that chitinases in Carrizo were induced in i nfested roots when the BCVC antibody was employed. These findings just ify calling these proteins pathogenesis-related proteins. The chitinas e that BCLVC was prepared from exhibited high lysozyme activities, and the results of western blots showed the presence of proteins at M(r) 24 000 and 27 000 which are presumed to be lysozymes. Similar tests us ing antibodies against beta-1,3-glucanases and peroxidases indicated a diminution of protein bands that cross-reacted with infested root pro tein extracts compared with what occurred in controls. All of the root extracts were tested against chitosans with various percentages of ac etylation; activities were linearly dependent on the amount of chitosa n acetylation; i.e. the larger the amount of acetylation, the greater the activity, Significant differences in hydrolase activities were obs erved between infested and uninfested roots for the rootstocks using t he variously acetylated substrates. All of the root protein extracts w ere capable of degrading peritrophic membranes removed from larvae of D. abbreviatus. This suggests that citrus chitinases may play a role i n disrupting the peritrophic membrane such that ingested substances th at pose a hazard to the insect may penetrate the membrane more easily.