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Volume 44 (2009): Issue 5 (Aug 2009) x
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Loren C. Stephens

Immature inflorescences of a Sorghastrum nutans (L.) Nash selection were cultured on CCm medium with 5 mg·L−1 2,4-dichlorophenoxyacetic acid and 1 mg·L−1 N6-benzyladenine (BA) for 5 weeks. Callused inflorescence cultures were placed on CCm medium with 1 mg·L−1 BA (CCmB1) and 0 or 250 mg·L−1 ethidium bromide (EtBr) for 24 h. Cultures were transferred to CCmB1 without EtBr for shoot regeneration and then to CCm without plant growth regulators for rooting. Rooted shoots were transferred to soil under greenhouse conditions and then to the field. Fifteen putative M1 mutants with atypical phenotypes were detected among 71 EtBr-treated regenerants. Two self-incompatible putative M1 mutants were progeny-tested by using a wild-type Indiangrass seedling as the pollen parent. M1 selection ISU06-35 was a dwarf mutant whose M2 testcross progeny segregated 1:1 tall:dwarf seedlings. M1 selection ISU06-56 was a red-flowered mutant whose M2 testcross progeny segregated 1:1 green-flowered:red-flowered seedlings. These results are consistent with both M1 mutants being dominant nuclear mutations.

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Alejandro Martínez-Bilbao, Amaya Ortiz-Barredo, Emilio Montesinos and Jesús Murillo

Fire blight, caused by the bacterium Erwinia amylovora, is among the three most important diseases of apple. A major effective method for its integrated management is the reduction of the susceptibility of the host. Cider apple production in Spain is based on local apple cultivars with minimum crop management and phytosanitary control. After the entry of fire blight in Spain, the selection and planting of cultivars with low susceptibility to this disease has thus become of paramount importance. In consequence, and as part of a wider characterization effort, we undertook the evaluation of an apple germplasm collection of local apple cultivars from Spain for susceptibility to fire blight. Because of the quarantine status of E. amylovora in Europe, we evaluated the use of a detached leaf inoculation assay in combination with a traditional shoot inoculation assay to reduce the amount of plant material to evaluate and to minimize pathogen manipulation. Comparison of the susceptibility values for 78 apple cultivars indicated a low but significant correlation (r = 0.56; α = 0.01) between the leaf and shoot inoculation methods. Although the detached leaf assay was not reliable for the direct selection of cultivars with low susceptibility, it was useful to optimize resources and limit the potential dispersal of the pathogen by allowing the exclusion of medium and highly susceptible cultivars from further evaluation. Shoot inoculation of 103 apple cultivars allowed the identification of 48 cultivars with high levels of resistance to fire blight, which could serve as starting material both for apple production and for breeding programs.

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Bradley S. Sladek, Gerald M. Henry and Dick L. Auld

Establishing turfgrass in shaded environments can create a unique maintenance challenge. Shading reduces zoysiagrass (Zoysia spp.) photosynthesis and results in reduced turfgrass aesthetic quality. Zoysiagrass is a warm-season, perennial turfgrass that forms a dense, uniform turf through the production of rhizomes and stolons. It has demonstrated good tolerance to growth in reduced light intensity environments. Greenhouse experiments were conducted in 2006 and 2007 to evaluate the relative difference in growth response to three light intensities (0%, 50%, and 90% shade) among six zoysiagrass genotypes under artificial shade conditions. Percent change in zoysiagrass plug diameter decreased as shade level increased 6 and 12 weeks after planting (WAP) regardless of year or genotype. ‘Diamond’ and ‘Shadow Turf’ exhibited the greatest percent change in plug diameter 12 WAP (60% to 69%) followed by the remaining zoysiagrass genotypes (21% to 56%) when grown under 50% shade, regardless of year. In 2006, no zoysiagrass genotype maintained acceptable turfgrass quality (6 or greater) 12 WAP when grown under 50% shade. However, ‘Diamond’ and ‘Shadow Turf’ exhibited acceptable turfgrass quality ratings (7.0 and 6.3) 12 WAP in 2007, whereas all other genotypes exhibited unacceptable turfgrass quality ratings (5.0 to 5.7). In 2006, ‘Shadow Turf’ zoysiagrass exhibited the greatest percent increase in plug diameter (21%) followed by ‘DALZ 0501’ (15%) and ‘Diamond’ (5%) 12 WAP when grown under 90% shade. All other zoysiagrass genotypes exhibited decreases in plug diameter (31% to 87%). In 2007, ‘Shadow Turf’ and ‘Diamond’ exhibited the greatest percent change in plug diameter (11%) followed by ‘DALZ 0501’ (7%) 12 WAP when grown under 90% shade. All other zoysiagrass genotypes exhibited decreases in plug diameter (17% to 38%). Turfgrass quality declined as shade level increased 6 and 12 WAP regardless of year or genotype. ‘Shadow Turf’ and ‘Diamond’ exhibited the highest turfgrass quality ratings (4.7 and 3.7, respectively, in 2006 and 5.3 in 2007) 12 WAP when grown under 90% shade. Proper zoysiagrass cultivar selection may improve turfgrass growth and quality under low light intensity while increasing turfgrass options for shaded environments.

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Tanya J. Hall, Jennifer H. Dennis, Roberto G. Lopez and Maria I. Marshall

In June to Oct. 2008, a U.S. floriculture survey was conducted to examine the factors affecting growers' willingness to adopt sustainable practices. The factors affecting adoption of sustainable practices were evaluated in five areas: environmental regulations, customer value, growers' attitudes toward sustainability, age, and operation size. A logistic regression model was used to examine factors affecting growers' adoption of sustainable practices. Nearly two-thirds (65.2%) of respondents thought sustainability was very important to the environment. Similarly, more than half (63%) of the respondents had sustainable practices in their operations. Although respondents had positive attitudes toward sustainability and the environment, these positive attitudes alone were unable to predict adoption behaviors. The two most important factors that affected adoption of sustainable practices were the concerns about implementation and the risk perceived by growers. Neither perceived customer value nor the stringency of state regulations affected the adoption of sustainable practices. The results from this study provide original insight into growers' views of sustainability and identify the educational assistance needed by growers to overcome the factors affecting their adoption of sustainable practices.

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Wei Hao, Rajeev Arora, Anand K. Yadav and Nirmal Joshee

Guava (Psidium guajava L.) is a tropical evergreen tree that tolerates a wide range of frost-free environments. In recent years, the American market demand for exotic and nutritious fruits, like guava, has been increasing, and, with a long harvest period, guava can be a potential alternative, high-value cash crop in the United States. However, the major limitation with commercializing guava cultivation in the United States is its low cold tolerance. In this article, we studied the physiology of freezing tolerance and cold acclimation in guava. Laboratory freeze–thaw tests (on leaves), shoot growth and leaf relative water content measurements, leaf anthocyanin content analyses, and leaf protein analyses were performed on nonacclimated and cold-acclimated guava cultivars Lucknow-49 and Ruby × Supreme. The leaf freezing tolerance (expressed as LT50 values) of nonacclimated tissues was ≈–2.5 °C and significantly enhanced to ≈–4.4 °C after an environmentally controlled cold acclimation regime for both cultivars. However, when compared based on actual injury sustained by leaves at various freezing temperatures in a freeze–thaw test, ‘Ruby × Supreme’ exhibited significantly less injury than ‘Lucknow-49’ at most temperatures. Growth and leaf relative water content reduced, whereas leaf anthocyanins accumulated during cold acclimation. Leaf protein analyses, which were performed after cold acclimation and drought stress, revealed that four proteins (69, 48, 23.5, and 17.4 kDa) accumulated in response to low temperatures, and two proteins (17.4 and 16 kDa) accumulated in response to drought stress. Antidehydrin immunoblots revealed that one common 17.4 kDa dehydrin accumulated in response to cold and drought stresses. Our data indicate that guava possesses leaf freezing tolerance, exhibits cold acclimation ability, and that ‘Ruby × Supreme’ leaves are relatively more freezing-tolerant than ‘Lucknow-49’ when compared up to –4 and –8 °C for nonacclimated and cold-acclimated tissues, respectively. Cold acclimation in guava appears to be a multifactorial process involving complex physiological and biochemical changes and also overlapping responses with drought stress.

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A. Maaike Wubs, Yuntao Ma, Lia Hemerik and Ep Heuvelink

Fruit set and yield patterns were studied in detail in six pepper cultivars. Fruit set differed largely between the cultivars: cultivars with small fruits (fruit fresh weight 20 to 40 g) showed higher fruit set (≈50%) than cultivars with large fruits (fruit fresh weight 120 to 200 g; 11% to 19%). The former showed continuous fruit set (four to five fruits/plant/week), whereas the latter showed fluctuations in fruit set. Fluctuations in weekly fruit set, expressed as the ratio between standard deviation of weekly fruit set and the mean of weekly fruit set (cv), were much lower for the cultivars with small fruits (0.44 to 0.49) than for the cultivars with large fruits (1.1 to 1.6). Fluctuations in weekly fruit yield varied between 0.51 and 0.77 for cultivars with small fruits and between 1.04 and 1.45 for cultivars with large fruits. Fluctuations in fruit yield were significantly positively correlated (Pearson R = 0.87) with fluctuations in fruit set. The correlation between fruit set and fruit yield patterns was highest with a lag time of 8 weeks for the cultivars with small fruits and 9 to 10 weeks for the cultivars with large fruits. This corresponds with the expected lag time based on the average fruit growth duration. The cultivars produced the same amount of biomass, implying that source strength was more or less similar. Hence, differences in fruit set and fruit yield patterns between the cultivars were not the result of differences in source strength and must therefore be related to differences in sink strength.

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Neil Anderson, Lee Klossner, Neal Eash, Vincent Fritz, Minnie Wang, Stephen Poppe, Judith Reith-Rozelle, David Wildung, Shengrui Yao, Patricia Johnson and Barbara E. Liedl

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Naser Lotfi, Kourosh Vahdati, Bahman Kholdebarin and Elaheh Najafian Ashrafi

Walnut (J. regia L.) is one of the most sensitive plants to abiotic stresses for which finding salt-tolerant genetic resources is very important. Effects of salt stress on seed germination of seven walnut cultivars (Serr, Lara, Pedro, Chandler, Hartely, Vina, and Roun de Montignac) were studied. Salt stress treatments were applied using NaCl solutions ranging from 50 to 250 mm. The increase in salinity levels resulted in a substantial decrease in root relative water content. The percent of germination was also affected by salinity level and cultivar and their interactions. The mean germination time differed among treatment media and cultivars and a significant interaction was observed between these two factors. According to the cluster analysis, ‘Chandler’ was classified as the most tolerant cultivar. ‘Hartley’, ‘Pedro’, and ‘Round de Montignac’ (‘RDM’) were also classified in another group (semisensitive), whereas ‘Vina’, ‘Serr’, and ‘Lara’ were classified as sensitive cultivars. With the increase in salt stress, resistant cultivars accumulated more potassium (K) and calcium, especially in their shoots. However, in the semitolerant cultivars, accumulation of K in the root was more than in the shoot. Differences in magnesium accumulation in roots and shoots of all samples were significant at all stress levels and were dependent on genotypes. Sodium levels in roots were higher than in the shoots in most cultivars, especially in the semisensitive and tolerant ones. There was a low correlation (r 2 ≤ 0.15) between walnut seed traits (seed weight and kernel weight) and growth indices with respect to salinity tolerance.

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Michael W. Olszewski and Grant J. Folin

Purpletop [Tridens flavus (L.) Hitchc.] and big bluestem (Andropogon gerardii Vitman) are incorporated into native grass seed mixes for use in ecological restoration. Alleviation of low seed vigor and poor stand establishment would benefit the restoration process by increasing the animal habitat in restored zones. This study determined the effectiveness of prechilling with distilled water (dH2O) versus potassium nitrate (KNO3), sodium hypochlorite (NaOCl) treatments, and short-term storage conditions on seed germination, seedling growth, and stand establishment of purpletop and big bluestem. Prechilling of ‘Niagara, NY Ecotype’ big bluestem for 7 days at 5 °C in dH2O increased final germination percentage (FGP) and germination rate provided caryopses were not dried before sowing. Optimal FGP, germination rate, and germination synchrony were obtained for ‘VA Ecotype’ purpletop after prechilling for 14 days at 5 °C in dH2O without subsequent caryopsis drying or at 0.2% KNO3 with or without subsequent caryopsis drying. Prechilling increased germination synchrony for purpletop but not for big bluestem. NaOCl treatments did not enhance germination or seedling vigor of purpletop or big bluestem. Using nonstored, prechilled caryopses resulted in greater root lengths than stored caryopses or nontreated controls, although optimal purpletop growth required that they be sowed moist, whereas optimal big bluestem growth required that they be dried-back before sowing. In greenhouse experiments, higher seeding rates were correlated with increased number of seedlings for nontreated or prechilled big bluestem and for prechilled purpletop, but not for nontreated purpletop, which had poor stand establishment at all seeding rates. The results indicate that prechilling of caryopses before incorporation into a warm-season grass seed mix increased seedling establishment of purpletop but not big bluestem.

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Justine E. Vanden Heuvel