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Identification of resistant cultivars offers the best control for Iris yellow spot virus (IYSV), a new onion disease vectored by Thrips tabaci. In this study, 18 spring-seeded onion cultivars were screened for IYSV. Each alternate plot in the field was planted with infected bulbs from the previous year to serve as a source of virus inoculum and thrips. With increased thrips population and temperature over time, straw-colored, necrotic lesions typical to IYSV infection were observed on plant leaves. Plants were analyzed by enzyme linked immunosorbant assay to confirm the IYSV infection and determine the virus titer. Ten randomly selected plants from each plot were rated for IYSV symptoms on a scale of 1 to 9, with 1 representing no symptomatic tissue and 9 representing more than 50% tissue damage. Starting 1 June, disease ratings were collected each week until 13 July. Nearly all cultivars showed similar disease symptoms when rated on 1 June. By 29 June, NMSU 03-52-1 exhibited some tolerance to IYSV as fewer symptoms were observed. By 13 July, NMSU 03-52-1 exhibited fewer disease symptoms than most of the other cultivars tested, while `Caballero' showed the highest IYSV symptoms. All other cultivars showed low to high susceptibility for IYSV. The increase in disease severity was accompanied by a relative increase in the virus titer of plants over time. However, virus titer poorly correlated with the amount of disease symptoms in different cultivars. The most tolerant cultivar, NMSU 03-52-1, had higher virus titer than many susceptible cultivars but still performed well. Conversely, some cultivars with low virus titer were susceptible and developed more symptoms. This indicates a difference in the capabilities of different cultivars to resist IYSV.
Abstract
A technique to induce early fruit maturation would permit staggering the harvest and provide an opportunity to avoid early fall rains which are common to grape growing regions with Mediterranean climates. Dipping trials with ethephon have resulted in advanced maturation in some cultivars of Vitis vinifera in Australia (2). The main effect observed was a decrease in total acidity. Weaver and Pool (4) observed that ethephon induced a significant increase in total soluble solids in ‘Carignane’ a wine cultivar but contrary results have also been reported (3). The present study was designed to determine the effect of ethephon on ‘Delight’, a table cultivar.
Greenhouse and field trials were carried out to evaluate carfentrazone as a potential tank mix with glyphosate to control weeds. Application of active ingredient glyphosate at 1.15 kg·ha−1 provided 44%, 50%, 19%, and 17% control of ivyleaf morning-glory, milkweed vine, hemp sesbania, and field-bind weed (stage 1), respectively, and increased to 45%, 51%, 31%, and 76%, respectively, with active ingredient of 2.30 kg·ha−1. Carfentrazone as active ingredient at 17.7 g·ha−1 achieved 53%, 90%, and 99% control of hemp sesbania, ivyleaf morning-glory, and milkweed vine (stage 1), and increased to 88%, 98% in first two weed plants, respectively, with active ingredient at 52.2 g·ha−1. Either rate of carfentrazone at any stages of field-bind weed yielded ≈100% control. Application of tank-mixed glyphosate and carfentrazone to ivyleaf morning-glory and hemp sesbania (stage 1) demonstrated greater control than their sole applications. A complete control of milkweed vine and field-bind weed (stage 1) was achieved by tank-mixed glyphosate and carfentrazone. Corresponding to percent control values a reduction in biomass value was also recorded. Biomass reduction with glyphosate at either stage of ivyleaf morning-glory was only 14%–24% and reduction with carfentrazone was 40%–47%. Biomass was further reduced with the tank-mixed glyphosate and carfentrazone. A similarly trend in biomass reduction was noted in milkweed vine and hemp sesbania. However, ivyleaf morning-glory was found to be the most tolerant weed to glyphosate followed by hemp sesbania, milkweed vine, and field-bind weed. Tank-mixed applications of these two herbicides further increased the percent control and biomass reduction. In all weed species, there was a significant decrease in percent biomass reduction with age. Although the types of weed were different in the field experiment and greenhouse, a similar trend was observed in the percent control achieved with glyphosate, carfentrazone, and their tank-mixed application. Tank-mixed applications achieved 93%–95% control of Brazil pusley and 75%–83% control of passion flower. These values were significantly higher than the percent control achieved with application of only glyphosate. Therefore, tank-mixed application of glyphosate and carfentrazone may be beneficial than sole application to control broadleaf weeds.
Onion growers in New Mexico often withhold irrigation for overwintered onion varieties during the months of December and January. This study was initiated to determine if this deficit irrigation program is detrimental to onion bulb quality. Twelve short- and intermediate-day onion cultivars, which differed in their maturity, were seeded in Sept. 2004 in Las Cruces, N.M. Once plants were established, 12 plots of each cultivar were not irrigated during the months of December and January (dry treatment), while the same number of plots was irrigated during these months (wet treatment). Once a plot had 80% of the plants with tops down, all bulbs were harvested, cured, and data on date of harvesting, bulb diameter, bulb height, firmness rating, number of centers, scale number, and scale thickness of first and third fleshy layers were collected. For most of the bulb traits measured, there was no difference between the two irrigation treatments for the cultivars tested. For the earliest-maturing cultivars, bulbs grown in the dry treatment had on average more fleshy scale layers than the bulbs grown in the wet treatment. For later-maturing cultivars, bulbs grown in the dry treatment had more growing points (centers) per bulb than the bulbs grown in the wet treatment. For the latest-maturing cultivars, average fleshy scale layer thickness was greater for bulbs grown in the dry treatment. From this work, a winter deficit irrigation program appears to be detrimental to the percentage of single-center bulbs for later-maturing, autumn-sown onion cultivars.
Depletion of the weed seed bank by stimulating germination during winter months and subsequently exposing the seedlings to adverse air temperatures is a possible means of controlling weeds in small-scale horticultural operations. Johnsongrass [Sorghum halepense (L.) Pers.], hemp sesbania [Sesbania exaltata (Raf.) Rydb. ex A.W. Hill], and barnyardgrass [Echinochloa crus-galli (L.) Beauv.] were seeded in soil trays and maintained for 4 days at 4 or -12 °C, then heated to 32 °C for 4 days using electric heating pads. Germination percentages, after heating soils, were: 55% and 70% for hemp sesbania, 82% and 72% for barnyardgrass, and 45% and 55% for johnsongrass, respectively; for seeds kept at -12 and 4 °C, respectively. Subsequent exposure of seedlings to -12 °C for 7 days killed all seedlings, while exposure to 4 °C killed only 18% to 28%. The temperature regimes of -12 °C for 4 days, and 32 °C for 4 days followed by -12 °C killed 95%, 78%, and 68% of the johnsongrass, hemp sesbania, and barnyardgrass, respectively.
Iris yellow spot (IYS) disease, caused by Iris yellow spot virus (IYSV), results in irregular and diamond-shaped, chlorotic, and necrotic lesions on the leaves and seedstalks of onions (Allium cepa L.). These lesions reduce leaf photosynthetic area and ultimately reduce onion bulb size and yield from larger bulb classes. IYSV is vectored by onion thrips (Thrips tabaci L.) that are difficult to control under certain environmental conditions. Currently, no onion cultivar is resistant to the disease symptoms, virus, and/or thrips. Twenty-one cultivars and 17 germplasm lines were evaluated in the field for IYS disease severity and thrips densities at multiple times during the season as well as leaf color, waxiness, and axil openness of these entries. Plants were grown under conditions that favored thrips populations (high temperatures, low moisture, and no insecticidal spray applications), IYSV presence and distribution, and IYS development. Plants of New Mexico State University (NMSU) 07-10-1 had fewer thrips than several entries later in the season in both 2009 and 2010. Several entries exhibited a lower number of thrips per plant early or later in the season; however, these results were not consistent across years and were not associated with a particular foliage characteristic. Lighter leaf color and/or a lesser amount of epicuticular wax did not always result in the fewest number of thrips per plant as has been reported in the literature. Plants of NMSU 09-58 tended to exhibit fewer and less severe IYS symptoms early in the season as compared with plants of other entries.
Multiple shoots were obtained from shoot tips (2 to 3 mm) derived from mature plants (5 to 6 years old) of Citrus reticulata Blanco cv. Khasi mandarin and C. limon Burm.f. cv. Assam lemon when cultured on Murashige and Skoog (MS) medium, supplemented with (mg·liter-1) 1.0 BAP, 0.5 kinetin, and 0.5 NAA. Root induction was observed when 7-week-old single shoots (≈ 2 cm long) of both Citrus species were cultured on MS medium supplemented with (mg·liter-1) 0.25 BAP, 0.5 NAA, and 0.5 IBA. These plantlets were successfully established in the soil. Chemical names used: naphthalene acetic acid (NAA), indole 3-butyric acid (IBA), and benzylamino purine (BAP).
Abstract
Container-grown Chinese holly (Ilex cornuta Lindl. Paxt. cv. Burfordii) and Japanese holly (Ilex crenata Thunb. cv. Helleri) were treated with 6 preemergence herbicides: alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl) acetanilide], napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide], oryzalin (3,5-dinitro-N 4,N 4-dipropylsulfanilamide), and oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] at 2.2, 4.5, 9.0, and 17.9 kg/ha; oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] at 1.1, 2.2, 4.5, and 9.0 kg/ha; and prodiamine [2,4-dinitro-N 3,N 3-dipropyl-6-(trifluoromethyl)-1,3-benzenediamine] at 4.5, 9.0, and 13.4 kg/ha. All herbicides at all rates significantly reduced the number and weight of weeds as compared to unweeded checks but higher rates were more effective. Lower rates of herbicides failed to control Pennsylvania bittercress, yellow wood sorrel, and purple nutsedge. Oryzalin at 9.0 and 17.9 kg/ha was phytotoxic to both hollies. Generally, Chinese holly was more tolerant to herbicides than Japanese holly. Oryzalin was most phytotoxic to Chinese holly and substantially reduced the growth and marketability of the plants. Oxyfluorfen at 9.0 kg/ha severely retarded the growth of Japanese holly.
Abstract
Alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl)acetanilide], napropamide [2-(α-naphthoxy-N,N-diethylpropionamide], oryzalin [3,5-dinitro-N 4, N4 -dipropylsulfanilamide], oxa-diazon [2-terr-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-∆2-l,3,4-oxadiazolin-5-one], each at 2.2, 4.5, 9.0 and 17.9 kg/ha, oxyfluorfen [2-chloro-l-(3-ethoxy-4-nitrophenoxy)-4-(trifluoro-methyl) benzene] at 1.1, 2.2, 4.5 and 9.0 kg/ha and prodiamine [2,4-dinitro-N 3, N3 -dipropyl-6-(trifluoromethyl)-l,3-benzenediamine] at 4.5, 9.0 and 13.4 kg/ha were evaluated for weed control and phytotoxicity in container-grown azaleas, Rhododendron indicum (L.) Sweet. ‘Formosa’ and Rhododendron obtusion (Lindl.) Planch. ‘Coral Bells’. All herbicides at all but the lowest rates effectively controlled grasses and broadleaved weeds. All herbicides at 9.0 kg/ha or higher rates were phytotoxic to these azaleas and restricted growth, root development and marketability. ‘Coral Bells’ was more susceptible to herbicide treatments than ‘Formosa’. Both azaleas were highly susceptible to oxyfluorfen.
Cultivated plants and their wild progenitors show marked phenotypic differences regarding seed dormancy, the ability to disperse seeds, growth habit, phenology, photoperiod sensitivity, etc. We have used RFLP mapping to investigate the genetic control of these differences in a recombinant inbred population derived from across between a snap bean and a wild bean. Traits were scored either at Davis or in Colombia. Our results suggest that the genetic control is relatively simple. In particular, most of the phenotypic variation (>60%) in the population could be accounted for in genetic terms for all but two traits. The genetic control of many traits involved genes with major effect (>30%). Some regions of the genome had major effects on several traits. Our results suggest that evolution can proceed by macromutations, domestication could have taken place fairly rapidly and introgression of additional genetic diversity could be itrogressed relatively easily from wild beans into the cultivated bean gene pool.