Factors affecting yield and other wheat characteristics at the La Platina Experiment Station, duringtheyears 1971 to 1981. II. Effectson yield of bread wheats

René Cortázar S.1

At the La Platina Experiment Station (INIA), severa) hundreds of bread wheat lineswerestudied in yield tria)s, under irrigation, every year between 1971 and 1981. In Part I of this paper, theeffects of severa) factors on the differences in yield between bread and durum wheats were analyzed; in this Part II, relations between yield of bread wheats and time of sowing; hectoliter weight; attack of Puccinia graminis, P. recondita, P. striiformis, BYDV, and aphids; accumulated degree-days (base 5ºC); and rainfali are studied. There were large differences in the average annual values for ah these parameters: yields varied between 26.6 and 92.1 quintals/ha; hectohiter weights, between 75.3 and 82.6; P. graminis infections, between traces and 47.4%; P. recondita infections, between 0 and 20%; P. striiformis infections, between traces and 8.5%; notes (0-absence; 10-maximum infection) on BYDV infection, between 0 and 10; notes on aphid infestation, between 1 and 8.
The main factors modifying yleid, in order of importance, were:

1. Date of sowing: years with early sowings gaye better yields;
2. BYDV: years with higher infectations produced lower yields; and
3. Aphids: years with larger infestations gaye lowsr yields.

Rainfali, hectohiter weight, commulative degree-days (base 5ºC), and P. graminis infections, showed no influence on yield.

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