RESISTANCE TO DOWNLOAD OF SORGHUM USING RTx430 AS A COMMON POLLINATOR OF LINES STERILE IN THE SHOAL

Abstract

Downy Mildew Peronosclerospora sorghi (Weston & Uppal) C. G. Shaw, is one of the most harmful diseases of grain sorghum in Mexico. An average loss of 3.5 ton/ha has been reported in susceptible hybrids in the State of Michoacan.

In 1979, 335 male sterile A lines differing in sensitivity to mildew were crossed with RTx430 restorer line (resistant to mildew) in order to study their hybrid reaction to this pathogenic organism. These hybrids were grouped into six field trials and evaluated in Maluco, State of Michoacan, in 1980; the B isogenic lines were also evaluated in this locations during 1981.

lt was found that approximately 75% of the B lines were moderately susceptible, and the remaining 25% reacted from moderately resistant to resistant. In the case of the hybrids, 70% were resistant, 20% moderately resistant, 5% moderately susceptible and 2% susceptible. Disease incidence was similar In both years, according to data obtained from proper checks.

The high proportion of resistant and moderately resistant hybrids in relation to their female parent response, suggests that the inheritance of resistance from RTx430 varíes from dominance to partial dominance.