Abstract
This study aimed to assess the impact of ethrel spraying on cassava leaf abscission at different stages of cultivar development. Two experiments were performed using randomized block designs, with 15 total treatments (three repetitions of five conditions) arranged according to the factorial scheme 3 x 5. Experiment 1 (ethrel application in the vegetative development period) consisted of three seasons (November 2013 and 2014, January and February 2014) and four concentrations of ethrel (1,500, 3,000, 4,500, and 6,000 ppm) and a control (no application); Experiment 2 (application in pre-harvest period) consisted of three periods of ethrel spraying (20, 40, and 60 days before harvest), four ethrel concentrations (1,500, 3,000, 4,500, and 6,000 ppm) and a control (without ethrel). The characteristics evaluated included the number of fallen leaves at 20 and 70 days after application, total leaf dry mass and foliar degreening. The effects of different concentrations and times of application of ethrel were significant during the first seven days. Ethrel application during the second period of vegetative development did not affect the number of fallen leaves over a period of 70 days.
Highlights
Leaf abscission is an important avoidance mechanism during water stress periods, which have become increasingly frequent and prolonged
We evaluated the number of fallen leaves, designated in this study as foliar abscission (FA), during the period 7 to 70 days after treatment (Experiment1) and 7 to 20 days after treatment (Experiment 2), the total leaf dry mass (TLDM), the foliar degreening and abscission velocity index (AVI) (Experiment 2)
For fallen leaf number and dry mass evaluated at 7 days prior to harvesting and at harvesting of plants that were treated at 20 days before the harvest date in relation to ethrel concentration, we found that the effects could be represented by a quadratic model, with maximum points at 4,365, 3,452, and 5,000 ppm, respectively (Figure4C, D, and F)
Summary
Leaf abscission is an important avoidance mechanism during water stress periods, which have become increasingly frequent and prolonged. The importance of this phenomenon is significant in cassava cultures, whose physiological resting period occurs at least once during cultivation (Liao et al, 2016). Our understanding of the cassava leaf abscission process has a broad and well-grounded knowledge base, and there has been strong interest in topics related to inducers of this phenomenon, such as water stress (Zhang et al, 2010; Duque & Setter, 2013), shortened photoperiod (Fagundes et al, 2009), and low (Schons, Streck, Kraulich, Pinheiro, & Zanon, 2007) and high temperatures (Akparobi, Tobih, Togun, Ekanayake, & Oyetunji, 2001).
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