Isolation of Phytoalexins from Corn with Monogenic Resistance to Helminthosporium turcicum

Genetics of Disease Resistance in Plants

“…Phytoalexins produced in response to pathogenic and nonpathogenic or ganisms have also been reported from soybean, maize, and other plants (90,(108)(109)(110) . Because the genetics of resistance is known in soybean and maize, these cases are more pertinent to this review.…”

“…No morphological barriers to the fungus have been observed in resistant plants (120) . It has been shown re cently that the resistance is due to production of phytoalexins in the resistant plant (109,110) .…”

“…In this case the inducer for phyto alexin formation seems to be produced only by the corn isolate of H. turcicum and the basis of resistance to the Johnson grass isolate remains unexplained. Two phytoalexins, Al and A2, are formed in resistant maize containing gene Ht (110). In several host-pathogen systems more than one phytoalexin has been isolated from the same resistant host, but so far only in maize has phy toalexin formation been limited to plants that have a major gene for disease resistance.…”

A Dominant Inhibitor Gene Inhibits the Expression of Ht2 against Exserohilum turcicum Race 2 in Corn Inbred Lines Related to B14

“…It has been proposed that the £. turcicum-Zea mays relationship fits the gene-for-genc model (LiM et al 1974). The gene-for-gene hypothesis assumes that resistance IS a positive function of the host and avirulence a positive function ot the pathogen (ELI.INGBOE 1979).…”

“…Necrosis is much delayed (HOOKER 1961) and there is an almost complete stippression of sporulation (HiLU et al 1963. The degree of resistance conferred by Ht depends on the genetic background in which it occurs (CALUB et al 1973a,, LiM et al 1970. The chlorotic reaction conferred by Ht is very convenient when selecting for its presence in segregating generations.…”