Symptoms In Cultivars Research Articles

Importance of temperature in evaluating cotton for resistance to Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum race 4

AbstractFusarium wilt of cotton (Gossypium spp.) is caused by a soil‐ and seed‐borne fungal pathogen Fusarium oxysporum f. sp. vasinfectum (FOV). Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4) is a significant threat to cotton production in the United States. The effect of temperature and soil on disease symptoms in cultivars with a range of susceptibility to FOV4 was examined in growth chamber trials. Three upland (G. hirsutum L.) and three pima (G. barbadense L.) cultivars were planted in three types of soils (potting mix and farm soils with and without FOV4 preinfestation) and maintained at four constant temperature regimes (20, 23, 26, and 29 °C). After seedling emergence, each pot was inoculated with conidial suspensions of FOV4 and scored for resistance based on disease incidence (DI), foliar disease severity rating (DSR), and mortality rate (MR) at 7, 14, 21, and 28 d post‐inoculation (dpi). The area under the disease progress curve (AUDPC) based on DSR across the four evaluation dpi was also analyzed. Among the six cultivars tested, Pima PHY 841 RF, Pima S‐6, and the uplands Acala 1517‐08 and FM 2334GLT were the most resistant, whereas upland PHY 725 RF and Pima S‐7 were the most susceptible. The genotypic responses to FOV4 were not significantly (P > .05) affected by differences in temperature regime or soil type. Cotton seedlings manifested more severe symptoms and higher mortality when maintained at 23 °C, followed by 20/26 °C and 29 °C in descending order. The mycelial growth rate was greater at 23/26 °C, whereas plants grew slower at 20/23 °C. There were no differences (P > .05) in DI, DSR, MR, and AUDPC between the inoculated farm soil (with no FOV4 preinfestation) and the inoculated FOV4‐preinfested farm soil, suggesting the unnecessity of using the latter in artificial inoculations. However, the potting soil produced higher (P < .05) DI and DSR at 7 and 14 dpi but lower (P < .05) AUDPC. This growth chamber study demonstrated that 23 °C produced the highest DI, severity, and plant death, providing an important piece of information for screening cotton for FOV4 resistance in breeding and FOV4 disease management in cotton production.

Molecular characterization and genome organization of temperature insensitive necrosis inducing strain of BCMV infecting common bean in India

BCMV strain NL-1n differing from already reported BCMV strains has been encountered on common bean in the entire North-Western Himalayan region. Unlike other strains of BCMV, this strain induced mosaic symptoms in cultivars possessing recessive “i” alleles and temperature insensitive necrosis (below and above 30 °C) on differential cv. Jubila carrying the dominant allele “I″. Despite the importance of the crop and the virus there is lack of genome information about any strain of this virus in the Indian subcontinent. In this study, complete genome sequence of NL-1n was determined to understand its relationship with other BCMV strains. The genome was 10,081 nucleotides long containing an open reading frame of 3222 amino acids that encoded a single polyprotein of approximately 365.99 kDa which is cleaved into ten proteins typical of Potyvirus. Pair wise comparison and phylogenetic analysis revealed that BCMV-NL-1n is more closely related to BCMV-NL-1 though clustered along with other strains and isolates of BCMV. Recombination analysis also revealed BCMV-NL-1n to be a recombinant showing two unique events. Based on these features, we propose to designate NL-1n as a recombinant of NL-1 and RU-1 strains. This is the first report of a BCMV strain inducing temperature-insensitive local necrosis on I gene carrying differential cv. Jubila as well as its complete genome sequence from India.

Cucumber vein yellowing virus isolate-specific expression of symptoms and viral RNA accumulation in susceptible and resistant cucumber cultivars

Since its outbreak in Spain during the fall of 2000, Cucumber vein yellowing virus (CVYV) has become into a limiting factor in cucurbit cultivation in this country, particularly in cucumber. The impact of the virus has been limited after the introduction of resistant cucumber cultivars and the implementation of cultural practices to control whitefly, the virus vector. In Spain, CVYV isolates are genetically similar and cucumber resistance breaking isolates have not been reported. A CVYV isolate from Jordan (Jor) was previously reported as being more virulent in cucumber cv. Beit Alfa than an isolate from Israel. To study the reactions of different cucumber cultivars to the virulent Jor isolate in comparison with a Spanish isolate of (Alm 1A), we have inoculated both isolates in 10 commercial cucumber cultivars with resistance to the virus. Also, we have used real-time RT-PCR to estimate virus accumulation of Jor and Alm 1A isolates in three of these cultivars, one described as susceptible and two as resistant to CVYV. The Spanish Alm 1A isolate caused mild or no symptoms in resistant cultivars whereas Jor isolate caused intense symptoms in all cultivars. Alm1 A genomic RNA accumulated similarly in the three cultivars, whereas the accumulation of Jor genomic RNA was lower in the resistant cultivars than in the susceptible cultivar. Also the Jor isolate and accumulated earlier and at a higher level than the Alm 1A isolate in the three cultivars.

A Strain of Peanut Mottle Virus Seedborne in Bambarra Groundnut

Peanut mottle virus (PMoV) was detected in nine of 95 bambarra groundnut (Voandzeia subterranea) plants grown in Florida from seed produced in Africa. This virus (PMoV-VS) induced systemic mosaic symptoms in cultivars of peanut (Arachis hypogaea), lima bean (Phaseolus limensis), and pea (Pisum sativum). PMoV-VS induced symptoms in differential bean (Phaseolus vulgaris) cultivars similar to those noted for an isolate of PMoV from the United States. PMoV-VS and PMoV induced very similar scroll, pinwheel, and laminated aggregate inclusions in infected leaf tissues. In immunodiffusion tests with PMoV-VS antiserum, precipitin lines of PMoV-VS and PMoV fused without spur formation (.)