Thermographic imaging to identify abscising apple fruitlets after a thinning treatment

Metamitron is a widely used active ingredient in pome fruit thinning. Its inhibitory action on photosynthesis determines a nutritional stress that in turn stimulates the weakest fruitlets to abscise. However, a successful thinning treatment with metamitron, commercially known as Brevis®, relies upon several interacting factors, both endogenous and exogenous, and its effects are difficult to predict under certain specific conditions. For this reason, new predictors are desirable to assist the growers in applying the treatment at optimal time and dosage. Moreover, the physiology of metamitron action is in part still unknown, especially at the fruitlet level. In the present research, a thermographic assessment was carried out to verify the hypothesis that high abscisic acid levels together with photosynthesis block in the fruitlet tissues cause the temperature to raise to higher levels in treated fruitlets than in the untreated ones. A specific trial was carried out in ‘Golden Delicious’, pointing out that both leaves and fruitlets of thinned trees show higher temperatures, which can be used to identify abscising fruitlets. A working model is also proposed that summarizes the way of action of Brevis® on both the considered organs