Factors affecting the survival and dissemination of Mycosphaerella pinodes (Berk & Blox) vestergr. in South Australian irrigated pea fields

Abstract

Results of trapping M. pinodes ascospores with a Hirst volumetric spore Trap during two successive crop seasons have demonstrated the pattern of variation of airborne inoculum in a South Australian irrigated pea field. Ascospore concentrations in the air above the field can be related to the presence of mature perithecia in residual crop debris and to the maturation of new perithecia on plants of the current crop. Wind tunnel experiments have shown that approximately 0.007 in. rainfall is the minimum for ascospore release, and that the peak liberation from mature perithecia occurred within 0 . 5 hr of wetting the straw. Results of experiments with straw burial treatments indicated that soil temperatures in the range 28–33°C, with high moisture, will cause a rapid reduction in the numbers of ascospores which may be discharged when the straw is unearthed subsequently. Examination of perithecia in straw which no longer discharged ascospores after such treatments, however, revealed that the perithecia, contained masses of dark-coloured spores quite distinct from normal ascospores.