COMPONENTS OF QUANTITATIVE RESISTANCE TO POWDERY MILDEW (ERYSIPHE-PISI) IN PEA (PISUM-SATIVUM)

Components of quantitative resistance in pea (Pisum sativum) to Erysip he pisi, the pathogen causing powdery mildew, were investigated. Conid ium germination, infection efficiency, latent period and conidium prod uction dynamics on cv. Quantum (quantitatively resistant) were compare d with those on Pania and Bolero (susceptible). There was an additiona l comparison in conidium germination experiments with the resistant cv . Resal. Quantitative resistance in Quantum did not affect conidium ge rmination, but infection efficiency of conidia on this cultivar was 34 % less than on the susceptible Pania. More conidia germinated on 5-day -old leaflets than on 15-day-old leaflets but the age of the plant did not affect percentage germination or infection efficiency. The length of the latent period did not differ between cultivars. Total conidium production (AUC) per unit leaflet area on Quantum was 25% less than o n Pania. The maximum conidium production per day (CMAX) per unit leafl et area on Quantum was 33% less than on Pania. The time to maximum con idium production per day (TMAX) was 10% longer on Quantum than on Pani a. The cv. Bolero, reported to be susceptible, also showed some degree of quantitative resistance, but this differed from that of Quantum. T otal conidium production was less on Bolero than on Quantum, but the c onidia on Bolero were produced sooner, and for a shorter period, than on Quantum. The stability of these responses was tested by analysing c omponents in three different temperature regimes and testing for inter actions with temperature, and with leaflet age. Temperature affected a ll conidium production variables. AUC per leaflet area was nearly seve n times as great and CMAX nearly 15 times greater at 23 degrees C than at 13 degrees C. TMAX increased by 1.5 times when temperature increas ed from 13 degrees C to 18 degrees C or 23 degrees C. Several interact ions occurred and these are described.