Temperature Factor Affecting the Abscission Response of Mature Fruit and Leaves to CMN-Pyrazole and Ethephon in `Hamlin' Oranges

Abstract

<jats:p>The effect of temperature on the ability of 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) and ethephon to induce ethylene evolution and abscission of mature fruit and leaves was determined using 3-year-old potted `Hamlin' orange [<jats:italic>Citrus sinensis</jats:italic> (L.) Osb.] trees in environment-controlled growth rooms in seasons 2001-02 and 2002-03. Ethylene evolution and abscission of CMNP or ethephon-treated fruit and ethephon-treated leaves were highly temperature dependent. Fruit detachment force (FDF) and fruit ethylene evolution were not affected by application of ethephon at 200 mg·L<jats:sup>-1</jats:sup> or CMNP at 200 mg·L<jats:sup>-1</jats:sup> when air temperature was 10 °C for ethephon treatment or ≤15.6 °C for CMNP treatment. However, ethylene evolution of CMNP or ethephon-treated fruit increased sharply, and FDF decreased drastically as temperature increased from 10 to 26.7 °C for ethephon treatment or from 15.6 to 26.7 °C for CMNP treatment. Several 10 hour day/14 hour night temperature regimes were explored to determine the effect of varying daily and nightly temperatures on efficacy and ethylene evolution. At least 3 days of exposure to 21/10 °C were required for CMNP to effectively loosen fruit, whereas only one day of exposure to 26.7/15.6 °C was enough to induce similar changes. At 21/10 °C, CMNP significantly reduced FDF to&lt;25 N and markedly enhanced fruit ethylene evolution, regardless of interruption by 1 day of low temperature at 10/10 °C in the first 5 d after application. Ethephon had no significant effect on leaf ethylene evolution and leaf abscission when temperature was 10 °C, but caused a marked increase in both leaf ethylene evolution and leaf abscission as temperature increased from 10 to 26.7 °C. CMNP did not stimulate leaf ethylene evolution and leaf abscission regardless of temperature. Chemical names used: 5-chloro-3-methyl-4-nitro-1 H-Pyrazole (CMNP); 2-chloroethylphosphonic acid (ethephon).</jats:p>

Oxidative Metabolism in ‘Valencia’ Sweet Orange (Citrus sinensis Osbeck) Abscission Zone Tissue Treated with the Abscission Agent 5-Chloro-3-Methyl-4-Nitro-1H-Pyrazole

“…PODs also act as IAA oxidases and can cause local decline in IAA levels (Henry, 1975). CMNP has been shown to elevate the levels of ethylene in citrus (C. sinensis Osbeck) and concomitant increase in fruit drop (Burns, 2002;Yuan and Burns, 2004).…”

“…CMNP is a pyrazole compound and demonstrated as a potential nontoxic abscission agent for the late season 'Valencia' sweet orange crop (Li et al, 2008). It has also been shown to aid in mechanical harvesting of citrus in Florida (Yuan and Burns, 2004). Several studies have been conducted to understand the mechanism of CMNP-induced loosening in mature citrus fruit (Kossuth et al, 1978;Li et al, 2008;Yuan and Burns, 2004).…”

“…It has also been shown to aid in mechanical harvesting of citrus in Florida (Yuan and Burns, 2004). Several studies have been conducted to understand the mechanism of CMNP-induced loosening in mature citrus fruit (Kossuth et al, 1978;Li et al, 2008;Yuan and Burns, 2004). Mechanisms of abscission vary among particular plant parts (Lewis et al, 2006).…”

Organ Loss and Yield Impacts of ‘Valencia’ Sweet Orange in Response to Fruit Abscission Agents

“…This amount of fruitlet loss may be close to a threshold compensation point beyond which yield reductions occur. The mode of action of CMNP is not yet known, but uncoupling activity and marked ethylene production were associated with its application in mature fruit (Alferez et al, 2005;Yuan and Burns, 2004). Nothing is known about CMNP-induced ethylene production in Response Periods I and II fruitlets.…”

“…Ethephon is an attractive second choice because it is currently registered for use on several food crops and is relatively inexpensive to apply. Previous work demonstrated that unacceptably high defoliation associated with ethephon applications, especially at high temperatures (Bukovac et al, 1969;Yuan and Burns, 2004), could be abated during the majority of the harvest season by coapplication of the ethylene binding inhibitor 1-methylcyclopropene (1-MCP; Pozo and Burns, 2000;Pozo et al, 2004).…”