Garlic (cv. Shani) was tested using single step RT-PCR and digoxygenin (DIG) labelled dot-blot for a number of viruses. Following sequence analysis it was shown that at least three different polymorphs of the potyvirus Onion yellow dwarf virus (OYDV) infect the same plant simultaneously, together with the potyvirus Leek yellow stripe virus (LYSV), the carlavirus Garlic common latent virus (GCLV) and a multitude of allexiviruses [Shallot virus X (ShVX) related viruses]. Several garlic plants free of all the viruses tested were obtained through meristem-tip culture. Plants infected with single viruses or with different combinations of viruses were similarly obtained. Meristem-tip culture was confirmed as a satisfactory method of virus eradication, while thermotherapy treatment given to mother plantlets before meristem excision was found to specifically antagonise OYDV eradication. This work uses molecular methods for the first time to examine the effectiveness of meristem-tip culture for the eradication of multiple viruses from garlic.
Four cultivars moderately resistant to Philippine isolates of Xanthomonas campestris pv . oryzae races 2, 3, 5 and 6 and highly resistant to race 1 were crossed with two susceptible cultivars and with each other . The F, populations were as or more susceptible than the least resistant parent cultivar when assessed for lesion length (cm) by clip-inoculating booting plants with two race 2 and one race 6 isolates of X. c. oryzae . The F2 populations showed continuous distributions when assessed with the race 6 isolate PX099, although populations from crosses between moderately resistant cultivars were positively skewed . Mean broad-sense heritability in the F2 was 0 .50 . Selection for varying levels of resistance was carried out in the F 2 and F3 generations . F 3 lines selected from the F2 population modes had variances and ranges equal to those selected from the F2 population extremes and larger than the variances of the parent cultivars .Line selection in the F 3 generation was more effective than plant selection in the F 3 and in the F 2. Realized h2 was 0 .39 for line selection in the F 3 but only 0 .24 for plant selection . A number of lines more resistant than both parents were recovered in crosses between moderately resistant cultivars . Lines more susceptible than both parents were also recovered in crosses between moderately resistant cultivars, but few of these lines were as susceptible as the susceptible cultivars . This indicates that the moderately resistant cultivars had some resistance factor(s) in common . All test cultivars, including the susceptible cultivars, carry few to several factors for quantitative resistance . A model based on nine minor resistance factors is proposed to explain the pattern of transgression found in crosses between the six cultivars .
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