Fungicide Sprays Can Injure the Stigmatic Surface During Receptivity in Almond Flowers

Spray and pray?

The topic of pesticide and fungicide residues on our food crops receives frequent attention in the media, and whatever our attitude to �organic� agriculture, a reduction in the level of possibly harmful compounds in food must be regarded as worthwhile. However, one aspect that usually escapes attention is the effect of pesticides and fungicides on the crop plants themselves. The work of Yi and colleagues (University of Georgia, USA, pp. 335-341) is directed at this very problem. They have worked on almond (Prunus dulcis), a tree that typically exhibits a fruit set of only around 30 % of flower number. Any further reduction would be economically undesirable. Almond is susceptible to blossom blight and trees in commercial orchards are sprayed with fungicides during the flowering season. Do these fungicides damage the flowers and thus reduce fruit set? The authors have studied the effects of controlled applications of four commercially used fungicides (at appropriate concentrations) to flowering shoots of almond. Control shoots were sprayed with similar volumes of water. Stigmas were then examined (without fixing) by SEM. The results of spraying varied slightly between the fungicides, but in general it was clear that spraying led to significant damage to the stigmatic surface. This damage included the production of a sticky exudate and the collapse of cells. The production of a stigmatic exudate in almond is normally associated with the phase of flower senescence. The authors suggest that the fungicides had caused a senescence-like process in the stigmas, a suggestion supported in those instances where cell collapse followed. These changes induced by the fungicides are very likely to reduce receptivity to pollen. Thus, the authors now wish to follow up these laboratory experiments with observations on plants sprayed in the field, focusing both on stigmatic receptivity and on fruit set.