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Ehiorobo Izekor and James O. Garner Jr.

Selected physiological and anatomical characteristics of four chilling-tolerant sweetpotato genotypes were evaluated. Although the genotypes were considered highly tolerant to chilling, it was proposed that differences in their mechanism for tolerance existed. A genotype temperature interaction for chlorophyll fluorescence ratio was observed when the plants were exposed to 5 °C. Genotype differences were found for electrolyte leakage and peroxidase activity. There were no differences found for fatty acid percentage composition of the glycolipid or the phospholipid fraction from leaf samples. There were no differences in diffusive resistance and transpiration rate among the genotypes; however, stomata density, leaf shrinkage, and specific leaf weight differed among the genotypes. Differences were also found among the genotypes for percent leaf dry weight, leaf thickness, and cellular structure of the leaf. It was concluded that the basis or mechanism for chilling tolerance was not the same for the four genotypes tested; therefore, combining traits for tolerance could lead to higher tolerance levels.

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Khin San Wai and S.E. Newman

The response of Antirrhinum majus (snapdragon) cultivars (`Tampicoi' and `Rainier White') to night air temperatures (10C and 20C) and elevated root-zone temperature (26C and ambient) was studied. Height of plants grown with a heated root-zone were greater, compared to unheated at both night temperatures for both cultivars. Shoot dry weight of `Tampico' plants was reduced by heated root-zone temperature at 20C night air temperature. Raceme length was greater with heated root-zone temperature compared to unheated at 10C night air temperature. Days to flower were shorter with heated compared to unheated root-zone at both night air temperatures for both cultivars. Stomatal diffusive resistance was greater on plants with unheated compared to heated root-zone temperature at 10C night air temperature for `Rainier White'.

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L.G. Sanabria and S.E. Newman

Various uniconazole (Sumagic™) rates were either sprayed or drenched alone or in combination with 6-BA and GA4+7 (Promalin™) or dikegulac-sodium (Atrinal™) on Hibiscus rosa-sinensis `Brilliant'. The rates of uniconazole were 0, 5, 10, and 15 mg a.i./L; 6-BA and GA4+7, 25 mg a.i./L each; and dikegulac-sodium 1000 mg a.i./L.

Plant height was reduced by uniconazole when drenched at rates as low as 5 mg/L and 15 mg/L when sprayed. Dikegulac-sodium slightly counteracted the effects of uniconazole. Uniconazole activity was increased when either sprayed or drenched with application of 6-BA and GA4+7 resulting in greater height reduction.

Transpiration and stomatal diffusive resistance of plants drenched with uniconazole alone was erratic; however, when uniconazole was sprayed or drenched and mixed with 6–BA and GA4+7 or dikegulac-sodium transpiration increased.

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Rufino Perez and Randolph M. Beaudry

Oxygen diffusive resistance of preclimacteric banana flesh is considered to be much lower than skin resistance such that negligible internal gradients in O2 are expected. Therefore, blocking O2 influx and CO2 efflux of banana by sealing 100% of the pores over fractions of one 1/4, 1/2, 3/4, and 7/8 of the surface, should generate an internal modified atmosphere similar to that achieved by using fruit coatings which cover 100% of banana surface but block only a fraction of the pores. Using gas trapping vials to determine internal O2 and CO2 levels, we followed O2 and CO2 behavior along the length of the fruit. Gradients for O2 and CO2 were found indicating sufficient flesh resistance exists to prevent consideration of internal resistances as negligible. Internal gas gradients were linked to ripening in that firmness and greenness were higher at the coated end. These results imply that banana flesh can not be treated according to the hollow sphere models previously suggested.

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D.J. Makus

A reflectant particle film material, `Surround', which also has biocide properties, and mycorrhizal root inoculation of tomatoes at transplanting were evaluated for their efficacy in improving tomato plant water status and agronomic performance in a supra-optimal, semi-arid environment. Seven-week-old `Heatmaster' tomato plants (Lycopersicon esculentum Mill.) were transplanted with or without a VAM inoculant (Gomes intaradices, Schenk & Smith) on 19 Feb. 1999 into a Raymondville clay loam soil in Weslaco, Texas (Lat. 26°12'). One-half of the inoculated and one-half of the uninoculated plants were sprayed between 16 Mar. and 1 June with seven applications of `Surround.' The trickle-irrigated plots were 5.6 m2 in size and treatments replicated four times in a RCB design. Recommended cultural practices were followed, but no fungicides were used. Results indicated that mycorrhizal treatment tended to accelerate fruit maturation and that particle film applications delayed fruit development relative to the control treatment. Mycorrhizal-treated plants had the highest yields at the second (of eight) harvest compared to the other treatments. There were no significant differences between treatments in leaf temperature, diffusive resistance, transpiration rate, water potential, and soil profile moisture, except between sampling dates. Fruit mineral nutrients, pigments, dry matter, average weight, total marketable and total season yields were not significantly effected by any treatment. When fruits were sectioned into proximal and distal halves, 10 out of 14 nutrients measured, in addition to dry matter, and total carotenoids were higher in the distal end.

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Rufino Perez and Randolph M. Beaudry

We hypothesized that the blocking of O2 influx and CO2 efflux in banana (Musa acuminata) by sealing nearly 100% of the pores over a fraction of the surface would generate a modified internal atmosphere in a manner similar to fruit coatings that cover 100% of the banana surface but only block a fraction of the pores. This hypothesis was based on the observation made by previous workers that the flesh of mature green bananas has insignificant resistance to O2 diffusion relative to the resistance imposed by the skin of the fruit. We modified the O2 diffusion pathway in bananas by covering, beginning at one end, ¼, ½, ¾, and ⅞ of the fruit surface with paraffin, which sealed essentially 100% of the surface where it was applied. Large end-to-end O2 and CO2 gradients developed within coated fruit, relative to the uncoated control, suggesting that the diffusive resistance in the pulp was not insignificant. Since the large gradients of O2 generated caused uneven ripening, using fractional coatings may help analyze gas exchange properties, but it is not suitable for commercially controlling ripening of bananas.

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Margaret J. McMahon, A.J. Pertuit Jr., and James E. Arnold

Leaves of chilled `Moss-Agate' Episcia (Mart.) plants exhibited direct chilling injury (i.e., watersoaked browning of leaf blade interveinal areas within 24 h of exposure to low temperature) immediately following exposure in darkness to 10C for 0.5 or 1.0 h. Chlorophyll fluorescence peak: initial ratios and terminal: peak ratios of chilled Episcia were -reduced 20% and 25%, respectively, 3 h after chilling, a result suggesting possible photosystem II damage. Total leaf chlorophyll content was reduced by 17% within 3 h of chilling and CO2uptake also was reduced at this time. Leaves of chilled `Rudolph Roehrs' Dieffenbachia maculata (Lodd.) (D. Roehrsii Hort.) plants expressed no visible injury within 24 h of 1.2C chilling in darkness for 36,48, or 60 h, but CO2uptake was reduced by 70% compared to the control 3 h after chilling. Visible injury began to appear 27 h after chilling, and the older leaf blades of all chilled plants exhibited a watersoaked appearance 75 h after chilling. Chlorophyll fluorescence peak: initial ratios of chilled Dieffenbachia did not vary, and terminal: peak ratios were not reduced until 147 h after chilling, when the injured tissue was extremely flaccid and translucent. Chilling reduced the chlorophyll content of Dieffenbachia by 10% in some plants 27 h after chilling and by 35%. in all plants 75 h after chilling. Transpiration rate was reduced and stomata] diffusive resistance increased 27 h after chilling.

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D.J. Makus

Kaolin cover sprays and mycorrhizal inoculation of tomatoes at transplanting were evaluated for their efficacy in improving tomato plant water status and agronomic performance in a supraoptimal, semiarid environment. Seven-week-old `Heatmaster' tomato plants (Lycopersicon esculentum Mill.) were transplanted with or without a vesicular-arbuscular mycorrhizal inoculant (Gomes intaradices Schenk & Smith) on 19 Feb. 99 into a Raymondville clay loam soil in Weslaco, Texas (lat. 26°12′). One-half of the inoculated and one-half of the uninoculated plants were sprayed between 16 Mar. and 1 June with seven applications of the kaolin-based particle film “Surround.” The trickle-irrigated plots were 5.6 m2 in size and treatments replicated four times in a RCB design. Commercial cultural practices were followed, but no fungicides were used. Results indicated that mycorrhizal inoculation tended to accelerate fruit maturation and that particle film applications delayed fruit development relative to the control treatment. Mycorrhizal (only) treated plants had the highest yields at the second (of eight) harvests compared to the other treatments. There were no significant differences between treatments in leaf temperature, diffusive resistance, transpiration rate, water potential, and soil profile moisture, except between sampling dates. Fruit mineral nutrients, pigments, dry matter, average weight, total marketable and total season yields were not significantly affected by any treatment. When fruits were sectioned into proximal and distal halves, 10 out of the 14 nutrients measured, in addition to dry matter, and total carotenoids were higher in the distal end.

Open access

Benjamin Paskus, Patrick Abeli, and Randolph Beaudry

the total) than when stored at NP (0.075% of the total). This is likely because LP facilitates diffusion of gases even in the interior of bulky tissues ( Burg, 2004 , 2015 ), diminishing the impact of the diffusive resistance in the bulky tissue and

Open access

Thomas M. Kon, Melanie A. Schupp, Hans E. Winzeler, and James R. Schupp

injury on leaf photosynthetic rate, diffusive resistance, and whole tree dry matter accumulation in apple HortScience 18 72 (abstr.) Francescatto, P. da Silva, A.L. Petri, J.L. Couto, M. Leite, G.B. Racsko, J. 2016 Quality of apple flowers grown in