Sweetpotato [Ipomoea batatas (L.) Lam.] roots of three Hawaii-grown cultivars (`Mokuau', `Okinawan', and `Yoshida') were treated with 0, 200, or 400 Gy x-ray irradiation and stored for 12 weeks at 15 °C. The storage quality of nonirradiated and irradiated roots was compared for weight loss, sprouting, firmness, color, postharvest decay, and carbohydrate concentrations. Nonirradiated roots lost 3 to 4% weight during storage, whereas roots treated with 400 Gy lost 4.7% to 8.6% weight. Sprouting was negligible for all treatments. Storage tended to increase root firmness, while irradiation tended to decrease firmness. When all cultivars were averaged, sweetpotatoes treated with 400 Gy and stored for 12 weeks had the lowest starch concentrations and highest total sugar concentrations. Glucose and fructose concentrations were not affected by irradiation, but these sugars increased during storage. Sucrose concentrations of roots irradiated with 400 Gy were double those of nontreated roots after 12 weeks storage. The purple-fleshed cultivars, `Mokuau' and `Okinawan', retained good quality following irradiation and storage, but firmness decreased somewhat for roots treated with 400 Gy. The `Okinawan' sweetpotato is the primary export cultivar from Hawaii. For the white-fleshed cultivar, `Yoshida', postharvest decay adversely impacted the internal color, firmness, and overall quality of roots treated with 400 Gy and stored for 12 weeks.
Marisa M. Wall
The fruit quality and ripening response of `Brazilian' bananas (Musa sp., group AAB) were determined following hot water immersion treatments for surface disinfestation. Summer-harvested fruit were exposed to 47, 49, or 51 °C water for 10, 15 and 20 minutes and ripened at 20 °C. The summer experiment established the exposure time and temperature limits for fruit injury. Winter-harvested fruit were immersed in 48, 49, or 50 °C water for 5, 10 and 15 minutes, stored for 12 d at 14 °C, and ripened at 22 °C. The hot water exposure time had a greater effect than the water temperature on banana fruit ripening. Nontreated bananas ripened after 13 to 15 d, and ripening was delayed by 2 to 7 d when fruit were exposed for 15 or 20 minutes to hot water. Hot water treatments did not inhibit pulp softening, but peels tended to be firmer for bananas immersed in 49 to 51 °C water than control fruit. Heat-treated bananas were not different from control fruit in soluble solids content or titratable acidity, however the conversion of starch to sugars was reduced at higher temperatures and exposure times. Bananas exposed for 20 minutes to hot water had delayed respiratory peaks and ethylene production, especially at 51 °C. Mild peel injury was observed on fruit exposed to higher temperatures (49 to 51 °C) for longer durations (15 or 20 minutes).
Marisa M. Wall
Sweetpotato [Ipomoea batatas (L.) Lam.] roots of two Hawaii-grown clones were treated with 100 to 600 Gy X-ray irradiation and evaluated for quality before and after cooking. Root moisture content, surface color, and glucose and fructose concentrations were not affected by irradiation treatment for either the red-skin, yellow-flesh (RY) or the white-skin, purple-flesh (WP) clones. Firmness decreased at higher doses for RY roots, but not for WP roots. The alcohol insoluble solids and the starch concentrations of raw roots decreased linearly in response to increasing dose for both clones. Maltose decreased at higher doses in cooked RY roots only. Irradiation had the greatest effect on sucrose concentrations, which increased linearly in response to dose as starch concentrations decreased. A sensory panel perceived sweetpotato roots treated with 600 Gy irradiation as sweeter than control roots. Panelists found the overall acceptability to be the same for control and 600 Gy treated roots for both clones.
Marisa M. Wall
Fruit quality and ripening of Dwarf Brazilian bananas (Musa sp., group AAB) were determined after x-ray irradiation for disinfestation of quarantine pests. The proximal and distal hands from winter- and summer-harvested bunches were treated with irradiation doses of 0, 200, 400, 600, or 800 Gy, stored for 7 days at 14 °C, and ripened at 20 °C. Irradiation did not extend banana shelf life or affect soluble solids content, but titratable acidity decreased with increasing dose. Starch and total sugar concentrations were similar for control and irradiated fruit at all doses. However, sucrose contents decreased linearly as dose increased, whereas glucose and fructose concentrations increased, indicating an acceleration of sucrose hydrolysis in treated bananas. Irradiation retarded peel softening but not pulp softening for winter-harvested fruit and had a minimal effect on peel and pulp firmness of summer-harvested fruit. For irradiated fruit, the respiratory climacteric rates decreased relative to control fruit, but CO2 and ethylene production increased 1 day after irradiation stress. Proximal fruit (more mature) had higher respiration rates and produced more ethylene than distal fruit (less mature) after irradiation, but differences in physiological maturity between hands did not affect soluble solids, titratable acidity, starch, or total sugar content of ripe fruit. Bananas from distal hands treated with 800 Gy irradiation developed peel injury when harvested in either the winter or summer months. Summer-harvested fruit also were damaged at the 600-Gy dose for distal fruit only. Treatment of fruit from the proximal half of bunches at doses ≤600 Gy would ensure visual quality while providing quarantine security for Dwarf Brazilian bananas.
Marisa M. Wall and Charles L. Biles
New Mexican chile peppers were harvested at weekly intervals beginning 105 days after planting (DAP), and evaluated for ethylene (C2H4) production, respiration rates, chlorophyll content, beta-galactosidase activity, polygalacturonase (PG) activity, and fruit firmness. Physiological changes were most apparent in peppers harvested 139-154 DAP. Beta-galactosidase activity increased rapidly beginning 147 DAP, and reached a peak of 24.5 mmol·gfw-1 when peppers were harvested 160 DAP. Polygalacturonase was not detectable at any stage of maturation. Fruit firmness was greatest (35.8 N) at 139 DAP and decreased significantly at 160 DAP. Carbon dioxide production and chlorophyll content were highest in young pods harvested 105 DAP, and decreased steadily thereafter. Ethylene production peaked (0.185-0.202 nl·gfw-1·h-1) in peppers harvested between 146-154 DAP.
Craig M. Hardner, Marisa Wall, and Alyssa Cho
Macadamia is a rapidly developing global crop; however, limited cultivation history and size of the industry means many challenges remain to support sustained productivity and profitability of this industry. This paper summarizes oral and poster presentations, and subsequent papers included in this volume, delivered at the 2017 International Macadamia Research Symposium, held in Hilo, HI, in September of that year. This was the first international meeting of macadamia researchers since 1992. The 28 oral and seven poster presentations covered propagation technology, tree physiology, soils and nutrition, pollination, pest and disease, orchard management, genetics and breeding, product development, and new production regions. Notable messages were that micrografting of macadamias is commercially viable; planting density and girdling could increase early yield per hectare; resource availability may limit cross-pollination yield; and yield production of individual branches is not independent. Integrated pest management was described to develop pest-resilient farming systems and manage felted coccid; an international collaborative approach was proposed for effective disease management and early detection; and the concept of integrated orchard management was used to translate research outputs into a common language for grower adoption. In the areas of breeding and genetic resources, research demonstrated that modern macadamia cultivars are two to four generations from wild but do not capture all wild diversity; progress was reported on the Macadamia Genome Project to produce the first macadamia reference genome; and advances in phenotypic selection and cultivar development were described.
Marisa M. Wall and Joe N. Corgan
Individual onion (Allium cepa L.) bulbs were evaluated for pungency by measurement of enzymatically produced pyruvate and by flavor perception. In four separate experiments, pyruvate values were highly and significantly correlated to mean sensory ratings. Correlation coefficients (r) were 0.92, 0.84, 0.95, and 0.79, and regression coefficients (R2) were 0.84, 0.71, 0.91, and 0.62. The high correlations indicate that pyruvate analysis can be used as a reliable selection technique for pungency in onion breeding programs.
Marisa M. Wall and Joe N. Corgan
A 2-year field study was conducted to evaluate the effects of maturity and storage on fresh-market onion (Allium cepa L.) quality. Four short-day onion cultivars (`NuMex BR1', `NuMex Sunlite', `NuMex Starlite', and `Buffalo') were seeded in early October each year. Bulbs were harvested at five times; the first and second harvests were when 20% and 80 %, respectively, of the bulbs in a plot had mature necks; the third, fourth, and fifth harvests were at 5,10, and 15 days after the second harvest date, respectively. After curing for 3 days, bulb firmness, weight, and incidence of disease were evaluated for all harvests. Bulbs were re-evaluated after 10 and 20 days storage in a shed under ambient conditions. `Buffalo' and `NuMex Surdite' bulbs had the lowest incidence of disease before storage. For all cultivars, average bulb weight increased and firmness decreased with delayed harvest. Percent diseased bulbs increased for all cultivars as harvest was delayed in 1991 but not in 1992. The optimum harvest time was at 80% maturity. In storage, average bulb weight and firmness decreased, and the incidence of bulb diseases increased.
Marisa M. Wall and Shakil A. Khan
The quality of three dragon fruit clones (Hylocereus spp.) was determined after x-ray irradiation for disinfestation of quarantine pests. Fruit were treated with irradiation doses of 0, 200, 400, 600, or 800 Gy and stored for 12 days at 10 °C. Irradiation did not affect soluble solids content, titratable acidity, or fructose concentrations. Glucose, sucrose, and total sugar concentrations decreased linearly as dose increased. Minimal softening occurred in the outer flesh layers for fruit treated with 400 or 600 Gy irradiation. Surface color, peel injury, and bract appearance differed among the three clones with irradiation stress, but in all cases, visible changes were minor. Fruit decay was absent or minimal, and disease ratings were not affected by irradiation. Irradiation treatment of dragon fruit at doses 800 Gy or less would ensure visual and compositional quality while providing quarantine security.
Arthur D. Wall, Marisa M. Wall, and Joe N. Corgan
Onions (Allium cepa L.) with ≥18% bulb dry weight are dehydrated and used for spices and food ingredients. Bulb weight characteristics and water-soluble carbohydrates (WSC) of two commercial dehydrator cultivars, GS02 and GS04, and a breeding population, NM9335, were studied before and after maturity to observe phenotypic traits that may be useful for selection during breeding programs, and to study dehydrator onion carbohydrate physiology. At maturity, NM9335, GS02, and GS04 bulbs had 11.9 ± 0.33%, 18.6 ± 0.27%, and 19.4 ± 0.40% dry weight, respectively. Mature GS04 plants had 76.5 ± 0.01% of whole plant dry weight in bulbs, which is an extraordinarily high crop harvest index. NM9335 bulbs had higher fresh (hydrated) weight than bulbs of GS04 and GS02, but bulbs in all populations accumulated similar amounts of dry weight. Bulb percent dry weight before maturity did not indicate percent dry weight at maturity in the high-solids commercial onion cultivars. Bulb percent dry weight declined slightly after maturity in all populations. Glucose, fructose, and sucrose were relatively low, and fructans with degree of polymerization ≥6 were relatively high in GS04, but the converse was observed in NM9335. Relative amounts of GSO4 bulb fructan increased sequentially, in order of rank, from DP4 to DP6, but the converse was observed for NM9335.