Relation between rainfail and temperature w-ith incidence of three wheat rusts, at La Platina Exp. Sta. Period 1965 to 1983

René Cortázar S.1

Correlations were determined between the average incidence of P. striiformis, P. recondita and P. graminis on several hundred wheat lines, under study each year, with rainfall and sum of degree-days (base 5º C), o different periods in the respective years. There were no correlations between degree-days and the incidence of P. striiformis and P. recondita, in any of the periods considered. A high correlation was found between degree-days in October and the incidence of P. graminis (r = 0.65). The incidence of P. striiformis was associated with rainfall in the first halt of August (r = 0.72) and in August (r = 0.69). P. recondita was associated with rainfall in the second half of September (r 0.76) and in September (r = 0.66). P. graminis was correlated with rainfall in the second half of November (r = 0.75) and in November (r = 0.79>. Correlations were also found between P. graminis and rainfall in the second half of July (r = 0.67) and in July (r = 0.58). Biologically it is difficult to explain these last correlations, because this fungus growths much later in the year; but the correlation found between rainfail in July and in November (r = 0.74), explains this apparent association. No other correlations were found in the periods studied.

1 Estación Experimental La Platina (INIA), Casilla 5427, Santiago, Chile.