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  • Author or Editor: George C. Martin x
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Adding Al2O3 to 8-hydroxyquinoline citrate (8-HQC) solution did not alter the sensitivity of the leaf abscission zone to external ethylene. Exogenous ethylene at 791 nl·liter-1 for 72 to 120 hours and at 193 nl·liter-1 for 120 hours induced leaf abscission, whereas no leaf abscission occurred at 47 nl·liter-1 for 72 to 120 hours. Ethylene at 791 nl·liter-1 for 72 to 120 hours increased ethylene evolution, but the amount of ethylene evolved from the explants does not seem to be enough to induce leaf abscission. Three different ethylene inhibitors—aminooxyacetic acid (AOA), CoCl2, and aminoethoxyvinylglycine (AVG)—were used to determine whether P-induced leaf abscission was mediated through elevated ethylene evolution. Although AOA and CoCl2 failed to inhibit ethylene evolution from the explants stem-fed with NaH2PO4, AVG inhibited ethylene evolution. Each inhibitor, except 5 mm CoCl2, promoted leaf abscission when administered alone or with P. Our results reveal that P-induced olive leaf abscission may occur without elevated ethylene evolution. At 40 or 75 mm NaH2PO4, abscission did not occur until explants were removed from N2 and placed in ambient air.

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Abstract

The acid methanol extract from the exocarp of l,2-l4C(2-chloroethyl)ohosphonic acid 14c-CEPA treated peach fruits contained 4 radioactive substances in addition to 14c-CEPA. In the petroleum ether extract 3 such substances were found. The total radioactivity of these substances, compared to the 14c-CEPA and its inherent contaminants recovered from the peach fruit exocarp, did not exceed 3%. Neither the petroleum ether nor acid methanol fractions contained a true metabolite of CEPA as a result of reactions involving living tissue. The nature of the radioactive fractions and their significance is discussed. Additional examinations were made on the stability of these fractions and their distribution in the fruit. Sugars were involved in the formation of one of the major radioactive fractions.

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Authors: and

Abstract

Penetration of ethephon into peach fruits was determined using l,2-14C(2-chloroethyl)-phosphonic acid (l4C-CEPA). Most of the activity accumulated in the fruit exocarp, with only minute amounts in the mesocarp. No notable lateral translocation was apparent. The results suggest that active degradation of the compound takes place in the young fruit while in the older peach fruits the rate of l4C-CEPA degradation takes place at a slower rate.

Open Access

Abstract

At “June drop”, the abscission zone occurs predominantly between the fruit and the receptacle. The abscising fruits had low levels of a growth promoter and high levels of a growth inhibitor, tentatively identified as ABA. Persisting fruits had higher levels of the growth promoter and lower levels of the growth inhibitor than did abscising fruit. Treatment of immature fruits with the chemical thinners 3-CPA or ethephon induced levels of growth regulators in the abscising fruits equivalent to those in abscising non-treated fruits.

Open Access

Foliar sprays of TIBA inhibited the growth of apple seedlings, and induced bitter pit of field grown `Golden Delicious' fruit. Total Ca levels were significantly decreased in the stems and leaves of apple seedlings, and in fruit peel. Foliar sprays of NAA increased total Ca content in shoots of apple seedlings. The Ca levels in the roots of seedlings were affected less by TIBA and/or NAA sprays than that of shoots. Irrigation after TIBA treatment inhibited apple seedling growth, and decreased total Ca content in shoots and roots, while NAA increased the growth and Ca content in the seedlings. TIBA via lanolin mixture to the shoot inhibited growth, and decreased the Ca content in shoots and roots of apple seedlings. NAA via lanolin mixture did not affect growth, whereas it increased the Ca content in the shoots of apple seedlings.

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We studied the effect on fruit and leaf abscission of application of ethephon (ETP) at 600 mg liter-1 on excised fruit-bearing olive (Olea europaea L.) shoots held under controlled conditions of temperature and relative humidity analogous to field conditions during fall harvest. Fruit removal force (FRF) and percent leaf drop (%LD) were quantified. Raising solution pH did not improve harvest effectiveness. %LD was significantly higher than control at pH 5, but not at pH 3 or pH 7; FRF was not significantly affected by pH. %LD was not significantly higher than control in the time-of-application treatments (pH 3 only); FRF was significantly less than control when applied at 7AM or 12 noon, but not at 5PM or 10PM. Addition of NAA to the ETP solution raised FRF and lowered %LD; BA had the opposite effect. BA accelerated anthocyanin production on fruits. Regardless of treatment, FRF and %LD are highly but negatively correlated (r2 = 0.62). Harvest effectiveness of ETP use on olive can be defined as a convergence of decreasing FRF and increasing %LD. Mean values for all ETP treatments were FRF = 3.0 N and %LD = 15%, acceptable values for effective olive harvest. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon); naphthalene acetic acid (NAA); 6-benzylaminopurine (BA).

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Under laboratory conditions foliar sprays of NaH2PO4 to olive explants induce fruit loosening with low percent leaf loss. In the field, NaH2PO4 foliar sprays are less successful in fruit loosening. Trunk injections of NaH2PO4 to olive trees in the field result in both leaf and fruit abscission. The lack of fruit abscission inducement from foliar sprays is thought to be due to poor chemical penetration. To improve penetration of NaH2PO4 several additives were tested to slow drying rate. These treatments led to increased fruit abscission over that of NaH2PO4 used without an additive. Even more fruit abscission was achieved with H3PO4 but this treatment led to fruit marking. Several additives were mixed with H3PO4 in addition to pH adjustment to ameliorate the fruit marking problem. The best current treatment combines H3PO4 with adjuvants such as Regulaid or Activator 90. It appears that adjuvant reduction of surface tension results in H3PO4 spread over more fruit surface, inducing less fruit making, while retaining the fruit abscission inducement feature desired.

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The addition of Al2O3 to 8-hydroxyquinoline citrate (8-HQC) solution did not alter the sensitivity of the leaf abscission zone to external ethylene treatment. Exogenous ethylene at 791 nl·l-1 for 72 to 120h and at 193 nl·l-1 for 120h induced leaf abscission whereas at 47 nl·l-1 for 72 to 120h no leaf abscission occurred. Ethylene treatment at 791 nl·l-1 for 72 to 120h increased ethylene evolution, but the amount of ethylene evolved from the explants does not seem to be enough for leaf abscission induction. Three different ethylene inhibitors, aminooxyacetic acid (AOA), CoCl2 and am inoethoxyvinylglycine (AVG), were used to determine whether phosphorus-induced leaf abscission was mediated through elevated ethylene evolution. Although AOA and CoCl2 failed to inhibit ethylene evolution from the explants stem-fed with NaH2P O4, AVG inhibited ethylene evolution. Each of the inhibitors except for 5 mM CoCl2 promoted leaf abscission when administered alone or with phosphorus. Our results reveal that phosphorus induced olive leaf abscission occurs without elevated ethylene evolution, but that oxygen is required.

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Record low temperatures were experienced in California during the last 10 days of December, 1990. Olive trees in both the Sacramento and San Joaquin Valleys suffered damage from the freeze. The lowest minimum recorded in these areas was -11.6C at Willows (Glenn Co.). Types of damage included death of succulent growing tips, defoliation, bark split, and bark and xylem discoloration. Tree death to the ground was uncommon. Defoliation continued throughout the growing season, and many leaves that persisted became chlorotic. Major outbreaks of olive knot disease caused by Pseudomonas savastanoi were seen in damaged trees, especially in `Manzanillo.' Anatomical studies showed evidence of ice nucleation events in the phloem, xylem, and leaves, but the cambium was usually left intact. Refoliation and healing of bark splits progressed rapidly once growth resumed in the spring, except in cases of olive knot infestation. Cultural practices that predisposed trees to freeze damage were those leading to late-season vegetative growth, namely fall pruning and late or excessive irrigation or fertilization. `Manzanillo' is the least cold-hardy of California cultivars and the most susceptible to olive knot. `Barouni' is the most hardy.

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Olive fruit harvest by mechanical shaking continues to be limited by poor fruit removal - less than 60% removal for most varieties. Whereas foliar spray of ethylene releasing compounds such as ethephon increases fruit removal percent, excessive leaf loss following treatment precludes commercial acceptance of the treatment. A classic case of serendipity has led to the testing of phosphorus as an olive fruit loosening agent. Na2 HPO4 at 25 mM applied via the cut stem of explants leads to massive leaf and fruit abscission. When the P source is applied at 100 mM foliar spray, fruit removal is accomplished with minimal leaf loss. Results of this investigation will cover P source, concentration, genera with abscission response and some indication of mechanism of action.

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