Florida Cultivars Research Articles

Genetic Base of U.S. Mainland Sugarcane

Evaluations of the genetic diversity of many crop breeding populations have been conducted in response to concern over their genetic vulnerability to diseases and insects. The purpose of this study was to evaluate the genetic diversity of U.S. mainland sugarcane (Saccharum L. spp.) cultivars. Eighty‐eight cultivars from Florida, Louisiana, and Texas were traced back to seventeen original ancestors. Coefficients of parentage (r × 100) were calculated among cultivars and ancestors. Cytoplasmic genetic sources were also traced. Ten ancestors contributed germplasm to 90% or more of Florida cultivars, whereas only two ancestors contributed germplasm to 90% or more of Louisiana cultivars. Mean coefficients of parentage for current commercial cultivars in Florida ranged from 8.2 to 18.6. For Louisiana commercial clones, coefficients of parentage ranged from 16.3 to 25.8. Cytoplasmic sources traced to three S. officinarum L. clones. The ancestor Black Cheribon (S. officinarum) contributed the greatest amount of nuclear and cytoplasmic germplasm. In comparison with many crops, sugarcane is probably relatively well buffered genetically.

Evaluation of Peanut Breeding Lines for Resistance to Silverleaf whitefly (Homoptera: Aleyrodidae)

Silverleaf whitefly, Bemisia argentifolii Bellows & Perring, n. sp., is a new and occasionally damaging pest of peanut, Arachis hypogaea L., in Florida and other southern states. In 1992 and 1993, elite germplasm from the peanut breeding program at the University of Florida and several commercial cultivars were evaluated for resistance to silverleaf whitefly. In 1992, 52 genotypes that were chosen based on their performance in previous trials were evaluated. Numbers of whitefly red-eyed nymphs on peanut genotypes differed significantly. However, only two genotypes supported fewer whiteflies (although not significantly) than the cultivar ‘Southern Runner’. In 1993, we evaluated selections of crosses between Florida parent material (81206 and 567A) and a North Carolina parent (GP-NC343) with multi-insect resistance. All selections tested had higher numbers of whitefly eggs and red-eyed nymphs than either ‘Florunner’ or ‘Southern Runner’. No resistance to silverleaf whitefly was found in the peanut germplasm tested.

Survivalof Xanthomonas campestrispv.translucensBetween Successive Wheat Crops in Arkansas

Reducing the level of initial inoculum may be a feasible means of controlling bacterial streak and black chaff of wheat caused by Xanthomonas campestris pv. translucens. The objective of this research was to determine the principal source of inoculum under Arkansas conditions. Using artificially infested seeds, a rifampicin-resistant mutant of the pathogen (strain 88-14 Rif ) was established in field plots of wheat cultivars Florida 302 (susceptible) and Terral 101 (moderately resistant) at two locations and in a plot of Florida 302 at a third location. Bacterial streak caused by strain 88-14 Rif developed in all plots. Strain 88-14 Rif was not detected in crop debris, soil, or possible alternative host plants in the field 3 mo after harvest at any location. No bacterial streak symptoms were observed at any location on Florida 302 planted with disinfested seed 4 mo after harvest. However, strain 88-14 Rif was isolated from one of 480 Florida 302 leaves assayed from one location at one sampling time. The percentage of harvested seed infested with strain 88-14 Rif 2 mo after harvest ranged from 9.8 to 37.7% for Florida 302 and from 0.3 to 5.3% for Terral 101. Under growth chamber conditions, transmission of seedborne strain 88-14 Rif to seedlings ranged from 4.0 to 24.5% for Florida 302 and from 0.0 to 0.2% for Terral 101. Under field conditions, however, strain 88-14 Rif was isolated only from one seedling of one Florida 302 seed lot. Based on the poor survival of the pathogen in the field and the relatively high percentage of infested seed and transmission to seedlings under growth chamber conditions for the susceptible cultivar, infested seed is suspected to be the principal source of inoculum

Molecular analysis of plants regenerated from embryogenic cultures of wheat (Triticum aestivum L.)

Total DNAs of plants regenerated from immature embryo-derived 2-month-old embryogenic calli of wheat (cultivars Florida 302, Chris, Pavon, RH770019) were probed with six maize mitochondrial genes (atpA, atp6, apt9, coxI, coxII, rrn18-rrn5), three hypervariable wheat mitochondrial clones (K', K3, X2), five random pearl millet mitochondrial clones (4A9, 4D1, 4D12, 4E1, 4E11) and the often-used wheat Nor locus probe (pTA71), in order to assess the molecular changes induced in vitro. In addition, protoplast-derived plants, and 24-month-old embryogenic and non-embryogenic calli and cell suspension cultures of Florida 302 were also analyzed. No variation was revealed by the wheat or millet mitochondrial clones. Qualitative variation was detected in the nonembryogenic suspension culture by three maize mitochondrial genes (coxI, rrn18-rrn5, atp6). A callus-specific 3.8-kb Hind III fragment was detected in all four cultivars after hybridization with the coxI gene. The organization of the Nor locus of the plants regenerated from Florida 302 and Chris was stable when compared to their respective control plants and calli. The Nor locus in regenerants of Pavon and RH, on the other hand, was found to be variable. However, Nor locus variability was not observed in 14 individual seed-derived control plants from either Pavon or RH sources. In Pavon, a 3.6-kb Taq I or a 5.6-kb Bam HI+ Eco RI fragment was lost after regeneration. In one of the RH regenerants, which lost a fragment, an additional fragment was observed.

Minilee and Mickylee are mini-watermelons with potential for the Australian market

The watermelon industry aims to produce fruit 2 10 kg, but supermarkets sell cut portions, so there may be a market for smaller fruit, between 2 and 4 kg. We tested several small-fruited watermelon cultivars to see if there was potential to establish a mini-watermelon industry. Minilee and Mickylee (ex Florida) were the best 2 cultivars; the fruit of 3 Taiwanese cultivars split under slight pressure, and the fruit of the cultivars Sugar Baby and Baby Fun were too heavy. Minilee and Mickylee were grown at plant densities between 5550 and 22 200 plants/ha. At 7400, 11 100 and 14 800 plants/ha, 70-72% of the Minilee fruit weighed between 2 and 4 kg. In contrast, at 22 200 plants/ha, 79% of the Mickylee fruit weighed between 2 and 4 kg, but at the other plant densities only 38-59% of the fruit were in this weight range. We conclude that Minilee and Mickylee are suitable cultivars for a mini-watermelon industry around Bundaberg and probably other parts of Australia where Florida cultivars are presently grown. Because the yield of fruit in the 2-4 kg range for Minilee was less sensitive to plant density than the Mickylee yield in this range, we believe that Minilee would be the better commercial proposition.

Effects of Leaf Rust and Septoria Leaf Blotch on Yield and Test Weight of Wheat in Arkansas

Leaf rust, caused by Puccinia recondita, and Septoria leaf blotch, caused by Septoria tritici, are the most serious foliar fungal diseases of wheat in Arkansas. This study was conducted to determine the relationship of leaf rust and leaf blotch severities at the soft dough stage to yield and test weight losses. Field experiments were conducted on three wheat cultivars during two growing seasons at two locations. For each cultivar, foliar fungicides caused differences in leaf rust and leaf blotch severities, yield, and test weight. Regression was used to determine the relationship of leaf rust and leaf blotch severities to yield and test weight losses. Average yield losses for cultivars Florida 302 and Rosen were 0.30 and 0.25% for each 1% increase in rust severity, respectively

Development of Septoria nodorum Blotch on Winter Wheat Under Two Cultivation Schemes in Maryland

Field experiments were conducted on soft red winter wheat cultivars Florida 302 and Coker 916 at three locations in Maryland over two seasons to assess the effect of cultivation schemes on Septoria nodorum blotch epidemics and the need for disease control. High-input cultivation (HIC) employed half the row spacing and 1.5-2 times the nitrogen fertility of conventional input cultivation. Subplots were inoculated with Stagonospora nodorum at different rates to develop various epidemic levels. Septoria nodorum blotch in the field was more severe on foliage but less severe on heads of Florida 302 than on Coker 916, regardless of the cultivation scheme. HIC tended to reduce disease severity and resulted in higher yields, regardless of cultivar. However, seed infection was either not affected or increased with HIC

Reproductive Development of Eight Wheat Cultivars and a Triticale as Influenced by Sowing Date

Vernalization generally is required for adaptation of winter cereals to temperate climates and is basic to breeding and selection of new cultivars. The objective of this study was to assess the reproductive development of eight winter‐sown wheat (Triticum aestivum L.) cultivars and a triticale (× Triticosecale Wittmack) as related to vernalization and heat accumulation using sequential sowing dates at four environments. The study was conducted at Gainesville, FL (29° 38′ N fat); Quincy, FL (30° 36′ N lat); and Griffin, GA (33° 15′ N fat), in 1987–1988 and was repeated at Gainesville in 1988–1989. Seed of cultivars were sown in field plots, beginning about 15 December and Continued biweekly through 1 March. Cold and heat units were computed from Class AB weather‐station air temperatures logged daily. Spring‐type wheat cultivars Florida 301, Florida 303, and Owens and Beagle 82 triticale developed spike primordia after ≈2 mo and headed in 100 to 120 d, irrespective of vernalization. Intermediate winter cultivars Florida 302, Hunter, and Phoenix had not initiated spikes by ≤3 mo, and headed only if sown on or before 15 February. In contrast to this response in 1987–1988, Hunter headed irrespective Of sowing dates at Gainesville in 1988–1989. Cultivars Coker 983 and Caldwell required vernalization, and headed only if sown by December in the warmer year (1988–1989) or if sown in December or January in the colder year (1987–1988). We conclude that spring‐type wheat cultivars and triticale reproduce normally without vernalization, and are adapted to a broad range of latitudes and sowing dates in southern USA. Winter‐type cultivars require vernalization and should be seeded in early winter at lower latitudes.

Effect of Successive Watermelon Plantings onFusarium oxysporumand Other Microorganisms in Soils Suppressive and Conducive to Fusarium Wilt of Watermelon

Five successive greenhouse plantings of watermelon cultivars Florida Giant (susceptible to Fusnrium wilt) and Crimson Sweet (moderately resistant and associated with soil suppressiveness) had different effects on the populations of Fusarium oxysporum f. sp. niveum, indigenous F. oxysporum, and various microorganism groups in the soil and on watermelon roots within four soils representing different suppressive and conducive conditions to Fusarium wilt. Pathogen populations were not affected by planting either cultivar in an induced suppressive soil developed by monoculture of Crimson Sweet or in a nonsuppressive Florida Giant monoculture soil [...]

Physiological Traits Associated with Grazing‐Tolerant Alfalfa

AbstractMany alfalfa (Medicago sativa L.) cultivars do not persist under long‐term, continuous grazing. This study was conducted to examine the variation of physiological traits that may contribute to grazing tolerance. Plants of the grazing‐tolerant cultivars Alfagraze and Travois and the grazing‐intolerant cultivar Florida 77 were grown from seed (Study 1) and from cuttings (Study 2) in the greenhouse. Populations from each cultivar that survived 2 yr of continuous grazing in the field were also tested in Study 2. Plants were clipped either frequently (weekly) or infrequently (every 4 wk) for 20 wk. Measurements of root total nonstructural carbohydrates (TNC), root weight, top and stubble herbage yield, and stubble leaf area were taken at Weeks 0, 2, 4, 10, 12, 18, and 20. No differences were noted between populations in Study 2. Under infrequent clipping TNC levels for all cultivars were higher at 4 than 2 wk after clipping. Florida 77 produced high TNC and root and top weights only under infrequent clipping but had low TNC and root weights under both clipping regimes, produced low top and stubble herbage dry matter, but maintained high stubble leaf areas under frequent clipping. Alfagraze produced and maintained high TNC and root weights under both clipping treatments, but produced high stubble dry matter and leaf area under frequent clipping. The genetic potential of a cultivar to store large amounts of carbohydrates may enhance its grazing tolerance, although stubble leaf area is probably important in allowing maintenance of total nonstructural carbohydrates under frequent defoliation.

Mango Sapburn: Components of Fruit Sap and Their Role in Causing Skin Damage.

Damage caused to the skin of mango fruit by contact with sap exuded from the cut or broken pedicel reduces consumer acceptance and storage life of the fruit. Mangoes of the Kensington cultivar are particularly susceptible to sapburn injury. On centrifugation, the fruit sap separated into two phases. Skin damage was caused predominantly by the upper non-aqueous phase. A major component of this phase was terpinolene which gave symptoms indistinguishable from sapburn injury when applied to the fruit surface. The same type of damage could be induced by the application of synthetic terpinolene when applied undiluted, diluted in hexane or as an aqueous emulsion. Non-volatile sap components separated by distillation were not damaging to mango skin. Sap exuded from the mango leaf petioles also contained terpinolene, but its concentration was less than 1% of the concentration in pedicel sap and this sap was not damaging to the fruit skin. The Florida cultivar Irwin is less susceptible to sapburn injury and the predominant terpene in its sap was identified as car-3-ene. When applied to Kensington skin, car-3-ene caused significantly less damage than terpinolene. We conclude that the primary cause of mango sapburn is entry of volatile components of the sap such as terpinolene through the lenticels, resulting in tissue damage and subsequent enzymic browning.

CHARACTERISTIC TEMPERATURES DETERMINATION FOR STRAWBERRY FREEZING and THAWING

Differential scanning calorimetry (DSC) was employed to determine the freezing and thawing behavior of two strawberry cultivar, Tioga and Florida, since reported thermophysic values for them were not found. Supercooling, complete solidification, minimum incipient melting, maximum incipient melting, and onset temperatures with a reliable range of accuracy were evaluated from DSC curve. the cryoscopic temperature, the most difficult determination from the thermograms, was calculated following a method that used only experimental DSC data. This temperature was dependent on the unbound water and soluble solids concentration, therefore the value obtained for each cultivar was different: -0.78°C for Florida cultivar with 89% of water and -1.41°C for Tioga cultivar with 87% of water. Temperatures were compared with literature values for other strawberry cultivars to analyze the validity of the results.

Within-Vine Distribution and Damage of Sweetpotato Weevil, Cylas formicarius elegantulus (Coleoptera: Curculionidae), on Four Cultivars of Sweet Potato in Southern Florida

The sweetpotato weevil (SPW), Cylas formicarius elegantulus (Summers) is the most economically important insect pest of sweet potato, Ipomoea batatas (L.) Lam., worldwide. Low level infestations reduce quality and marketable yield (Proshold 1983). Terpenoids that are produced by sweet potato in response to SPW feeding may make even slightly damaged roots unfit for human consumption (Uritani et al. 1975, Akazawa et al. 1960). Yield losses of up to 60-80% have been attributed to SPW (Hua 1970, Subramaniam et al. 1977, Mullen 1984). Economically effective control measures for SPW in regions with large resident populations are lacking. There are no insecticides that will adequately control weevils in an infested field (Stall et al. 1984) because SPW immature stages are spent within vines and/or roots. For this reason, other SPW management approaches, such as host plant resistance, have been explored (Waddill & Conover 1978, Mullen et al. 1980a,b, 1981, 1982, 1985). With one exception (Waddill & Conover 1978), resistant cultivars have not been field tested in regions with high SPW population pressure. The present study was conducted to evaluate SPW resistance in four sweet potato cultivars in southern Florida, a region with a dense SPW population. Also, we determined the -impact of a mechanical barrier (polyethylene mulch) on field plant protection from SPW. Lastly, we compiled preliminary data on the within-vine distribution of SPW in sweet potato. The experiment was conducted in 1986 at the Tropical Research and Education Center in Homestead, Florida. Four sweet potato cultivars, I. batatas cv. Resisto, Regal, Sumor, and NC1135, were planted in a split-plot design with three replications. Plastic polyethylene mulch (white/black, 38 microns thick covering a 0.9-m bed width) was the whole-plot factor and cultivar was the split-plot factor. Cultivars were handplanted on 22 April in raised beds with 1.8 m centers. Slips (0.3-m long) of each cultivar were planted 0.3 m apart in one row per bed. Replicate plots consisted of 40 slips

Morphological Identification of St. Augustinegrass Cultivars1

A vegetatively propagated crop such as St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] should consist of distinctive, easily identifiable cultivars. The purpose of this study was to improve identification criteria for this species and measure the frequencies of various St. Augustinegrass cultivars in Florida. Morphological traits were recorded in 242 unknown Florida St. Augustinegrass lawn and sod samples, which had been transplanted and grown outdoors in containers with 16 known clonal cultivars and taxonomic representatives. Lawn and sod samples conformed mostly to the expected morphological distributions of ‘Floratam’, ‘Bitterblue’, and a heterogeneous ‘Roselawn’‐like complex. The latter clones were distinctive because of their intermediate‐sized (4.6 to 4.8 ram) spikelets, relatively long floral regions (measured from the base of the lowermost spikelet to the tip of the inflorescence), and long, narrow internodes. Therefore, they were named the Longicaudatus (“long‐stemmed”) Race. Clones with short (<4.5 mm) spikelets were also distinctive and were named the Breviflorus Race, however, this race was virtually absent in Florida. Spikelet length and length of the floral region separated known cultivars in 84 of 91 pairwise comparisons (P<0.05), and these two traits showed no detectable environmental variance between containers and field plots. Inclusion of floral traits in discriminant analysis increased the proportion of unknown clones that could be identified from 49% (with vegetative traits only) to 95%. Keys using vegetative field traits and replicated container measurements were 93% accurate in identification of knowns, and 86 to 96% consistent with discriminant analysis in identification of unknowns.

Evidence for the accumulation of a germination inhibitor during progressive thermoinhibition of seeds of celery (Apium graveolens L.)

The germination of seeds of celery (Apium graveolens L.) becomes progressively thermoinhibited on incubation in the dark at high temperatures, the inhibitory temperature being dependent on the cultivar used. In two high-dormancy cultivars of celery, the production of germination inhibitors in seeds incubated in the dark at 26°C gradually increased over a 7-day period. Inhibitor production was measured by incubating seeds of the low-dormancy cultivar Florida 683 in homogenates of the thermoinhibited seeds of the high-dormancy cultivars and recording germination either in the light or with the gibberellins A4 and A7 (GA4/7) in the dark. Most Florida 683 seeds which failed to germinate in the homogenates after 15 days were induced to germinate by addition of N6-benzyladenine (BA). The presence of BA in addition to GA4/7 throughout incubation in the dark completely overcame the inhibitory effects of homogenates. This indicates that thermoinhibition of celery seeds is associated with the accumulation of a germination inhibitor which interacts with cytokinins. This does not appear to be abscisic acid (ABA) since ABA levels in thermoinhibited seeds were lower than in untreated seeds and did not increase with duration of high temperature treatment.

Consumption and digestion of four cultivars of Solanum melongena by Selepa docilis larvae (Lepidoptera: Noctuidae)

The consumption and digestion of two Ghanaian eggplant cultivars (Asesewa and Odwanhwoa) and two exotic cultivars (Black Beauty and Florida Market) by larval Selepa docilis were studied in the laboratory. Daily food consumption was highest on Asesewa and lowest on Florida Market. Total food consumption was significantly highest on Asesewa, followed by Odwanhwoa, Black Beauty and Florida Market. The dry weight of food consumed per unit of larval fresh weight per day was highest on Asesewa, followed by Odwanhwoa, Florida Market and Black Beauty. In general, food consumption was higher on the Ghanaian than on the exotic cultivars. The efficiency of food digestion was significantly higher on the Ghanaian than on the exotic cultivars. Growth of S. docilis larvae, recorded by the daily larval fresh weights, was highest on Asesewa, followed by Odwanhwoa, Black Beauty and Florida Market. The conclusion is made that S. docilis is best adapted to Asesewa, then Odwanhwoa, Black Beauty and Florida Market. Furthermore, S. docilis is better adapted to the Ghanaian than to the exotic cultivars.

MINUET WEIGELA

Minuet is a hardy, attractive, dwarf, freely flowering, Weigela florida cultivar.

Physiological Aspects of Peanut Yield Improvement1

Development of new peanut (Arachis hypogaea L.) cultivars over the past 40 years has more than doubled yield potential. The purpose of this paper is to identify and evaluate the physiological changes made in the course of this varietal improvement that are responsible for the great increase in yield potential. Weekly harvests of large samples of four Florida cultivars, a Spanish peanut type, and one soybean (Glycine max (L.) Merr.) cultlvar gave the information needed to show the progressive changes in dry weights of all plant parts throughout the growing season. Other weekly samplings and observations gave numbers of pegs, flowers, and fruits as well as fruit weights, root length, shoot length, and leaf areas. Quantitative estimates of the physiologlcal factors responsible for the dry weight differences were made by computer simulation using the PENUTZ model. Differences in three physiological processes explain most of the yield variation among the five peanut cultivars; the partitioning of assimilate between vegetative and reproductive parts, the length of the filling period, and the rate of fruit establishment. Of these, the partitioning of assimilate had the greatest effect on fruit yield. Estimates of partitioning to fruit ranged from 41% in the first cultivar released to 98% in the most recently released cultivar. Crop growth rates did not differ significantly among peanut cultivars but all were much higher than the crop growth rate of soybeans.

A Simulated Selection Experiment in Sugarcane1

Two objectives of the experiment were: 1) to estimate the probability that the best clones in the test would be retained in selection at various intensities for stalk diameter, stalk length, stalk number per plant, and Brix in single‐stool sugarcane (Saccharum L.) cultivar tests; and 2) to see if subpopulations obtained by selection were superior to the unselected population. Twenty randomly selected sugarcane seedlings from the Florida cultivar development program were clonally propagated by single‐bud cuttings and transplanted to an 18‐block field test with a single plant of each clone per block. The following were later determined for each plant: stalk diameter, stalk length, stalk number per plant, and Brix. Within each block, the 20 plants were ranked for each of the four traits. The ranks were than used to simulate selection within each block at the 5, 10, 15, … 100% levels for each trait. In addition, means for each clone over all blocks were obtained and ranked. In selection at the 5% level (selection of the one best plant per block) the plant of the clone with the best overall mean was retained in 50%, 31%, 28%, and 36% of the blocks for stalk number, Brix, stalk length, and stalk diameter, respectively. For each trait, stringent selection yielded subpopulations averaging better than the unselected population. As we would expect because of environmental variation, some clones that averaged good over all blocks did poorly in one or more individual blocks. It was less common for clones with poor averages over all blocks to excel in an individual block. It was concluded that the population improvement possible with single‐plant sugarcane selection warrants increased use of single‐plant tests.

Cold Acclimation of Florida Peach and Nectarine Cultivars1

Abstract ‘Early Amber’ peach and ‘Sungold’ nectarine (Prunus pérsica (L.) Batsch) growing in north central Florida acclimated sufficiently to cold to withstand −14° to −15°C although day temperatures were above 20° and night temperatures were above 7°. Rest and acclimation to cold in short chilling cultivars occur at higher temperatures than in long chilling ones. However, Florida cultivars also become acclimated to a lesser degree. Wood chips taken from the trunks of ‘Early Amber’ trees in January survived −10°C but were killed at −13°. Young trees were killed at −11° but survived −10° in January. Subsequent death of tissue occurs as a result of low temperature stress.