Compounds that modulate the synthesis of gibberellin (GA) can also enhance resistance to abiotic stress in treated plants. Seed treatments of 600 ppm trinexapac-ethyl (TE), which inhibits GA synthesis by blocking the transformation of GA20 to GA1 and foliar applications of 15 ppm paclobutrazol (Paclo), which inhibits the oxidation of ent-kaurene to kaurenoic acid, were applied separately or together to three varieties of hot pepper (Capsicum annuum L.) that are popular in Thailand. Greenhouse-grown plants were subjected to 7-10 days of drought, and then rewatered before transfer to a screenhouse. Khee Noo (an upright “bird type” pepper) was most sensitive to drought, compared to Bang Chang and Hot (“cayenne type”). In all varieties, both Paclo and TE treatments reduced the height of irrigated plants, but led to the retention of both plant size and pepper yield in droughted plants, compared to either irrigated plants or to untreated droughted plants. Treatment with Paclo provided the greatest retention of leaf relative water content (RWC) under drought conditions, with no advantage to the combination Paclo+TE treatment. Only Paclo treatment increased leaf thickness in Bang Chan and Hot, whereas both Paclo and TE had similar effects on increasing leaf thickness in Khee Noo. Khee Noo was the variety most responsive to Paclo or TE treatments, with increases in leaf thickness, epicuticular wax, and leaf pigments, all of which may better allow the plants to survive stress by storing leaf moisture, enhancing photosynthesis (chlorophyll), and preventing oxidative injury (carotenoids). Electrolyte leakage, indicative of membrane permeability and thus of susceptibility to stress, was diminished by 25% to 33% in leaves from plants treated with Paclo or TE.
Lop Phavaphutanon*, Yonit Hebbe, Shlomo Cohen, and Joshua D. Klein
Susan Lurie, Joshua D. Klein, and Ruth Ben Arie
A prestorage heat treatment of 38C for 4 days applied to `Granny Smith' apples (Malus domestics Borkh.) before regular air storage at 0C inhibited the development of superficial scald. Heat-treated apples stored for 3 months had superficial scald levels similar to diphenylamine (DPA)-dipped apples, while all nontreated control apples had scald. After 5 or 6 months of storage, this inhibition of scald development by prestorage heat treatment declined. The prestorage heat treatment inhibited the accumulation of α-farnesene and conjugated trienes in apple cuticle during storage, while DPA inhibited only α-farnesene oxidation. This treatment may be a substitute for chemical treatments against scald not only for short-term storage of `Granny Smith' but possibly also for other scald-susceptible apple cultivars.
Joshua D. Klein, William S. Conway, Bruce D. Whitaker, and Carl E. Sams
`Golden Delicious' apples (Malus domestica Borkh.) were treated after harvest with heat (air at 38 °C for 4 days or 42 °C for 1 day) or 2% CaCl2 (w/v; applied as a dip or pressure-infiltrated) or a combination of the two and stored at 0 °C for ≤6 months. Decay caused by Botrytis cinerea Pers.:Fr. after inoculation to a depth of 2 mm with a conidial suspension virtually was eliminated in stored fruit heated at 38 °C, regardless of Ca treatment. Apples punctured to a depth of 0.5 mm (but not 2 mm) and inoculated with B. cinerea on removal from storage were almost completely protected from poststorage decay if they had previously been pressure-infiltrated with 2% CaCl2, regardless of the heat regime. Heating fruit at 42 °C and dipping in 2% CaCl2 were only partially effective in preventing decay from either pre- or poststorage inoculations. Fruit firmness was not related to resistance to decay.
Joshua D. Klein, William S. Conway, Bruce D. Whitaker, and Carl E. Sams
`Golden Delicious' apples (Malus domestica Borkh.) were treated postharvest with heat (38C/4 d or 42C/24 h) or 2% CaCl2 (applied as a dip or pressure-infiltrated) or a combination thereof and then stored. Decay caused by Botrytis cinerea was virtually eliminated in fruit heated at 38C after inoculation prior to storage, regardless of Ca treatment. Apples inoculated upon removal from storage were almost completely protected from decay if they had been previously pressure-infiltrated with Ca, regardless of heat regime. Heating at 42C or Ca dips were only partially effective in preventing decay. Pressure infiltration of Ca (regardless of heat regime) or heating at 38C (regardless of Ca treatment) resulted in firmer fruit (68 N) than Ca dips or heating at 42C (56 N), which were firmer than nontreated fruit (52 N).
Susan Lurie, Elazar Fallik, Joshua D. Klein, Frerenc Kozar, and Kornel Kovacs
Postharvest heat treatments were applied to three apple (Malus domestica Borkh.) cultivars: `Anna', `Golden Delicious', and `Jonathan'. The temperatures ranged from 38 to 50 °C and from 5 to 96 hours. The temperatures of 50 °C for 5 or 10 hours and 46 °C for 10 hours controlled all developmental stages of San Jose scale on `Golden Delicious' and `Jonathan' fruit. Blue mold germination was prevented by 46, 42, and 38 °C after 28, 34, and 42 hours, respectively. The time needed to control the fungus was longer than that required to kill the insect. Apples were damaged by a 50 °C treatment but could withstand at least 12 hours at 46 °C and at least 24 hours at 42 °C. At 38 °C no damage was found on preclimacteric apples even after 96 hours, but if postclimacteric fruit were heated at 38 °C heat damage occurred. The treatments that did not cause damage maintained the fruit firmness during post storage ripening. The results are discussed in the context of developing integrated postharvest heat treatments.
William S. Conway, Wojciech J. Janisiewicz, Joshua D. Klein, and Carl E. Sams
The viability of Penicillium expansum Link conidia in sporulating culture declined rapidly when exposed to 38 °C, and when conidia were exposed to 38 °C prior to inoculation of apple fruits (Malus ×domestica Borkh.), the resulting lesions were smaller than those on fruit inoculated with nonheated conidia. `Gala' apples were heated after harvest (38 °C for 4 days), pressure infiltrated with a 2% solution of CaCl2, or treated with the antagonist Pseudomonas syringae van Hall, alone or in combinations to reduce postharvest decay caused by Penicillium expansum. After up to 6 months in storage at 1 °C, no decay lesions developed on fruit that were heated after inoculation with P. expansum, or any combination of P. expansum, antagonist, or Ca. Parallel lots of heat-treated and nonheated fruit that were either infiltrated or not infiltrated with Ca were stored up to 6 months. They were then inoculated with P. expansum alone, or with the antagonist followed by P. expansum. Prior heat treatment did not influence lesion size. Calcium alone, the antagonist alone, and heat plus Ca all reduced the incidence of decay by ≈25%, whereas heat plus the antagonist reduced it by 70%. Calcium plus the antagonist or Ca plus the antagonist and heat reduced decay incidence by 89% and 91%, respectively. The integrated strategy of heat-treating fruit, followed by Ca infiltration and then treatment with an antagonist, may be a useful alternative to controlling postharvest decay with fungicides.