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Umedi L. Yadava

Fully developed and ripe guava (Psidium guajava L.) fruits harvested during Sept-Dec 1993, from field-grown trees which were winter protected by 6-mil clear polyethylene, were examined for physical characteristics and nutrient contents. The purpose of this study was to establish optimum harvest time, fruit yield and physical characters, and nutritional fluctuations over a five week storage time. Fruits picked at turning stage, were observed for fresh weight, fruit girth (horizontal) and height (vertical), fruit volume, and fruit surface & flesh color evaluation (L* a* b* values by chromameter CR-200, Minolta Corp). Nutritional analysis (proximates, vitamins, and minerals) of fruits harvested on Oct 11, Oct 18, Oct 25, Nov 1, and Nov 8 and, refrigerated until analyzed, was performed at Food Science Department, University of Georgia. There were 342 fruits/tree with an average weight of 292 g, fruit girth 26.1” and height 7.5”. L* a* b* values for surface and flesh colors were. +65.61. -6.86, +39.37, and +55.86, +35.41, +19.48, respectively. Nutritional analyses indicated that the guava fruits were high in vitamin C (305 mg per 100 g fruit). K (201 mg), protein (1.4 g) and total dietary fiber (5.1 g) but low in fat (0.19 g per 100 g fruit) and Na (1.3 mg). The harvested fruit kept well for a five weeks period under refrigerated storage. Except for a modest loss of moisture, the storage period showed no significant effect on nutrient contents in the proximates, vitamins or mineral analyses indicating value of cool storage for guavas.

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Umedi L. Yadava

Seeds of a pink flesh test line of guava (Psidium guajava L.) from India, were germinated in a greenhouse. In April 1988, 6-month-old guava seedlings were set 3 m apart in a field row while an equal number of plants in 15 liter containers, were held in the greenhouse. The field plants were more vigorous than those held in the greenhouse. However, the field plants could not survive severe winter conditions outdoors and were totally destroyed by winter freezes of 1989-90. In spring 1990, the plants held in greenhouse were transplanted in the field under a 6-mil polyethylene protective cover where they flowered during February-April 1991. Trees were productive with 52 fruits per tree, most of which reached maturity without a drop or pest problems. Fruit ripening on trees began in late August 1991. Values for such parameters as fruit weight, height from blossom end to stem end, circumference and volume were 269.3 g (±10.6), 7.3 cm (±0.1), (25.6 cm (±0.3), and 279.7 ml (±11.4), respectively. Actual values ranged from 117 to 597 g, 5.5 to 10.1 cm, 19.3 to 33.2 cm, and 131 to 639 ml, respectively. Tree-ripe fruits had pink tinge on yellow-green skin and pink colored thick flesh had mild aroma and good flavor. Guava can be successful in Middle Georgia with proper care for cold protection.

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Umedi L. Yadava

A planting of 90 Redhaven peach (Prunus persica (L) Batsch) trees either budded to Lovell and Nemaguard rootstocks or on their own roots, was established in spring 1984 using in-ground 55-gallon microplots. Planting soils (top soil, not B and C layers) prepared in five ratios by mixing soils from peach tree short life (PTSL) and non-PTSL (NPSL) sites (100% PTSL, 75% PTSL + 25% NPSL, 50% of each, 25% PTSL + 75% NPSL, and 100% NPSL) as main plots, were replicated 3 times. Two trees per rootstock were randomized within main plots. The planting was maintained using conventional cultural practices. Observations for tree survival were recorded in December each year. During this investigation, both soil mix and root types significantly affected tree survival, which was consistently the highest in 100% NPSL and the lowest in 100% PTSL soil. Effects of other soil combinations were intermediate; however, greater tree mortality was associated with increased ratio of PTSL soil. Trees on Lovell roots invariably survived the best followed by those on Nemaguard roots and the lowest when on their own roots. As early as in fourth leaf, >55% of the own-rooted trees died compared to < 10% on either rootstock.

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Renee M. Harber, Andrew P. Nyczepir, Umedi L. Yadava, and Ronald R. Sharpe

The effects of rootstock, pruning, and preplant soil fumigation on floral bud dormancy status and shoot cold hardiness of `Redhaven' peach [Prunus persica (L.) Batsch] trees were monitored. Dormancy status, expressed as percent floral budbreak, was significantly affected by rootstock and pruning, although differences were small. In late January, significant interactions occurred between rootstock and pruning treatments, as well as between pruning and soil treatments. Pruning of trees on Lovell rootstock resulted in significantly lower budbreak as compared to trees on Nemaguard and unpruned trees on Lovell. Also, for trees pruned in December, higher budbreak was associated with those growing in fumigated vs. nonfumigated soil. Treatment effects on dormancy status did not correspond with treatment effects on hardiness. In fact, differences in hardiness were minimal and probably not biologically meaningful.

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Freddi A. Hammerschlag, Richard H. Zimmerman, Umedi L. Yadava, Sally Hunsucker, and Petya Gercheva

A range of antibiotics and short-term exposure to an acidified (pH 3.0) medium were evaluated for their effects on eliminating Agrobacterium tumefaciens, supervirulent strain EHA101 (pEHA101/pGT100), from leaf explants of `Royal Gala' apple (Malus ×domestica Borkh.) and on shoot regeneration. Exposure of leaf explants to regeneration and elongation media containing 100 μg·mL-1 concentrations of the antibiotics carbenicillin (crb), cefotaxime (cef), and cefoxitin [=mefoxin (mef)], singly or in combination for 52 days did not eliminate A. tumefaciens from the explants. The percentage of regeneration on crb, cef, and mef was 97%, 11%, and 50%, respectively, compared to 67% for the controls. Short-term (1- to 18-hour) vacuum infiltration with 500 μg·mL-1 of any of the above antibiotics did not inhibit regeneration and failed to eliminate A. tumefaciens from leaf explants. Cef (2000 μg·mL-1) did not inhibit the percentage of regeneration and was more effective than crb or mef in preventing growth of A. tumefaciens when vacuum infiltrated into apple leaf explants for 30 minutes. Further experiments demonstrated that the incidence of A. tumefaciens contamination could be reduced to 28% without negatively impacting shoot regeneration by using a 1-hour vacuum infiltration with an acidified medium, an 18-hour vacuum infiltration with cef (5000 μg·mL-1), and a 52-day incubation on regeneration and elongation media containing 100 μg·mL-1 each of mef and crb. Kan resistant, GUS (β-glucuronidase) positive, putative transformants without A. tumefaciens were generated by adding kan (10 μg·mL-1) to the regeneration and elongation media.