WOUND PREDISPOSITION OF MAIZE TO ANTHRACNOSE STALK ROT AS AFFECTED BY INTERNODE POSITION AND INOCULUM CONCENTRATION OF COLLETOTRICHUM-GRAMINICOLA

A 2-yr study was carried out to ascertain the nature of wound predisposition of maize to anthracnose stalk rot (ASR) relative to internode position and inoculum level. Stalks of hybrids Cornell 281 (susceptible) and CM174 x LB31 and B37 x LB31 (resistant) were inoculated with 1-ml suspensions of 10(2), 10(4), 10(6), 10(7), and 10(8) conidia of Colletotrichum graminicola per milliliter into wounds at midwhorl or anthesis and immediately or 6 hr after wounding. For each inoculation regime, the most severe ASR developed in the susceptible hybrid. At each inoculum level, the most severe ASR resulted from inoculation at anthesis and immediately after wounding. Disease severity increased with increasing inoculum up to 10(7) conidia per milliliter in greenhouse-grown plants and up to 10(6) conidia per milliliter in field-grown plants. Genotypic, ontogenic, and "wound heating" resistances to ASR were expressed in maize even at high inoculum levels of C. graminicola. Systemic ASR resulted from inoculation immediately after wounding of any of the first five internodes above the brace roots, but wound healing restricted considerably systemic ASR after inoculation of aged wounds in the lowermost stem internodes.