Inheritance of resistance to the papaya ringspot virus-watermelon strain from two different accessions of winter squash Cucurbita maxima Duch.
Inheritance of resistance to the papaya ringspot virus-watermelon strain (= PRSV-W, syn. watermelon mosaic virus-1 = WMV-1) was studied for two Cucurbita maxima accessions – ABL-010 and Redlands Trailblazer – considered to be resistant to the potyvirus. ABL-010 (ABL) derives its resistance from Brazilian accessions of C. maxima. Redlands Trailblazer (RT) is an Australian cultivar of C. maxima, the resistance of which traces back to C. ecuadorensis. In both cases, virus could be recovered from the inoculated (symptomless) plants via back inoculation onto susceptible C. pepo cultivar Caserta, indicating a tolerance type of resistance. Both ABL and RT were crossed to each other and to the standard PRSV-W-susceptible cultivar Buttercup (B). For each one of the crosses (ABL ×> B), (ABL × RT) and (RT × B), parental lines, F1, F2 and backcrosses to both the parents (BC1P1 and BC1P2) were tested for PRSV-W resistance after mechanical inoculation. Seedlings were inoculated at the first true leaf stage with a known PRSV-W isolate in 0.02 M phosphate buffer (pH 7.0) plus sodium sulphite 0.01%. Plants were scored for virus symptoms 28 days after inoculation; symptom severity being rated with a scale from 0 (= no symptoms) to 5 (= plants with severe mosaic and leaf distortions). Broad and narrow-sense heritabilities of PRSV-W resistance were 0.44/0.36, 0.59/0.59 and 0.58/0.58 for crosses (ABL × B), (ABL × RT) and (RT × B), respectively. Resistance imparted by ABL in cross with susceptible B could be explained by the action of three genes with partial dominance. Resistance imparted by RT in cross with B was found to be under control of at least two genes with additive effects. Susceptible plants were found in segregating populations of the cross ABL × RT (transgressive segregation), indicating that at least one of the loci involved in the control of resistance in ABL was not allelic to their counterpart loci in RT. The resistance imparted by RT appears to be of higher level than that imparted by ABL.
Overview of Potyvirus resistance in watermelon
Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] is a major cucurbit crop that accounted for 7.5 % of the world area devoted to vegetable production in 2003. Potyviruses are a major limiting factor in commercial watermelon production worldwide. The major viruses affecting watermelon are Papaya ringspot viruswatermelon strain (PRSV-W), Watermelon mosaic virus (WMV), and Zucchini yellow mosaic virus (ZYMV). Sources of resistance to PRSV-W have been reported. These were PI (plant introduction) accessions from South Africa (PI 244017, PI 244018, PI 244019), from Zimbabwe (PI 482342, PI 482318, PI 482379), from Botswana (PI 485583), and from Nigeria (PI 595203). A single recessive gene controls resistance to PRSV-W, with the gene symbol prv. Resistance to WMV is a quantitative trait in watermelon, with approximately 3 major loci involved. PI 595203 is resistant to ZYMV, and is also moderately resistant to WMV. The USDA germplasm collection of 1613 PI accessions was screened for resistance to the Florida strain of Zucchini yellow mosaic virus (ZYMV-FL). A high level of resistance to ZYMV-FL was found in several accessions: PI 386019, PI 490377, PI 596662, PI 485580, PI 560016, PI 494528, PI 386016, PI 482276, and PI 595201. The study also confirmed the resistance of PI 595203, PI 386025, PI 386026, and PI 494528 that was reported previously. Resistance of PI 595203 was confirmed to the three potyviruses PRSV-W, WMV, and ZYMV, so it will be useful in the development of multiple-virus resistant cultivars. Inheritance of resistance to Zucchini yellow mosaic virus-China strain (ZYMV-CH) and ZYMV-FL in PI 595203 was reported to be controlled by a single recessive gene. Further research is needed to determine whether resistance genes for ZYMV-FL in PI 482261 and in PI 595203 are allelic. INTRODUCTION Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is a major cucurbit crop that accounts for 7.5 % of the world area devoted to vegetable production in 2003. Worldwide, watermelons are grown on over 3.7 million ha and produce more than 83 million Mg of fruit. A rough estimate of annual world value of watermelon exceeds $15 billion. Watermelon is grown in more than 96 countries worldwide. China is the world leader in watermelon production with 70.3 % of the total Cucurbitaceae 2008, Proceedings of the IX EUCARPIA meeting on genetics and breeding of Cucurbitaceae (Pitrat M, ed), INRA, Avignon (France), May 21-24, 2008
Efficiently establishing concepts of inferential statistics and hypothesis decision making through contextually controlled equivalence classes.
Computerized lessons that reflect stimulus equivalence principles were used to teach college students concepts related to inferential statistics and hypothesis decision making. Lesson 1 taught participants concepts related to inferential statistics, and Lesson 2 taught them to base hypothesis decisions on a scientific hypothesis and the direction of an effect. Lesson 3 taught the conditional influence of inferential statistics over decisions regarding the scientific and null hypotheses. Participants entered the study with low scores on the targeted skills and left the study demonstrating a high level of accuracy on these skills, which involved mastering more relations than were taught formally. This study illustrates the efficiency of equivalence-based instruction in establishing academic skills in sophisticated learners.