Relationships among wheat yield, fungal diseases and environmental variables in the north of the Argentinean Pampas.

MILISICH, H.; CAVIGLIA, O.P.; SALUSO, J.

Mar del Plata - Argentina

Conferencia; 7th International Wheat Congress.; 2005

Wheat yield potential is positively related to intercepted solar radiation and negatively to temperature. Photothermal quotient (Q), obtained as the ratio between these variables, is therefore the most widely used index to predict potential grain number per unit area. However, attainable yield in fields without irrigation and fungal control, may be related to other environmental conditions no considered in classical approaches of yield potential. The aim of this work was to evaluate the relationships among yield, disease infection and environmental variables registered in several crop development stages. Average data of yield, its numerical components, data of anthesis, maximum leaf rust (Puccinia triticina) infection and Fusarium head blight (Fusarium spp.) infection index (HBII) of 61 experiments, carried out during 9 years (1996-2004) at Paraná in the north of Argentinean Pampas (31º5’S, 60º3’W), were recorded. Four crop periods were considered: a) vegetative, b) spike growth period (SGP), i.e. from 21 days previous to 7 days after anthesis, c) grain filling and d) from emergence to physiological maturity. Interrelationships among environmental variables and experimental data during those periods were evaluated using correlation analysis and linear regression. The most relevant variable associated to yield, although negatively, was rainfall during SGP (p<0.0001, r=-0.66) which, in turn, was positively associated to HBII (p<0.0001, r=0.61). Maximum leaf rust infection was not associated to yield. Excluding data with HBII>5%, the negative relationship between rainfall during SGP and yield was still significant (p<0.0001, r=-0.40; n=41), probably due to higher minimum temperature average associated to rainfall (p<0.0005, r=0.52; n=41) and consequently to a lower Q. When rainfall during SGP was lower than 40 mm, the HBII was negligible. In that data-set, correlation (r=0.76) between yield and rainfall during March previous to the crop planting (p<0.0001, n=28) was also detected. In fact, 68% of residuals were negative when March rainfall was lower than 120 mm, otherwise 73% of residuals were positive. Probabilities of heavy rainfalls during SGP increased as anthesis date was delayed. Agronomic strategies, oriented to improve yield, its stability and profitability, should be based on an adequate choice of anthesis date in coincidence with low rainfall and freeze probability, coupled with an adjustment of crop management according to autumn rainfall records, in order to maximize returns through matching inputs and attainable yields.