MSUIR Collection:

Diallel analysis and characterisation of verticillium wilt tolerance in cotton (gossypium hirsutum l.)

Chapera, Blessing — 2014-11-01T00:00:00Z

Title: Diallel analysis and characterisation of verticillium wilt tolerance in cotton (gossypium hirsutum l.) Authors: Chapera, Blessing Abstract: Cotton production is generally declining due to several limitations which include climate variations, poor crop management and biotic stress factors. Of the biotic stress, diseases are a major limiting factor of cotton production. Verticillium wilt is one of the most important disease and is an economically important fungal disease causing significant losses to seed cotton yield in Zimbabwe. Varietal development for resistance in cotton requires the understanding of the underlying genetic control of Verticillium wilt tolerance. Resistant breeding material against the disease is available but further improvement has to be done on other traits of economic importance. Thus, five local varieties with varying tolerance to the disease and different yield potentials were crossed in a half diallel mating design in 2013. This was done in order to elucidate the inheritance pattern and gene action of the resistance traits of the cotton lines. The ten crosses and five parents that were produced by the mating system were screened against Verticillium wilt by artificial inoculation at Cotton Research Institute, Kadoma in a glasshouse in 2014. These cotton lines were characterised using agronomic and morphological markers to identify Verticillium wilt resistance gene movements from parent lines to offspring. The trial was laid out in a completely randomised design with three replications due to the homogeneity conditions that prevailed in the glasshouse. Screening for Verticillium wilt resistance was done using a disease severity scoring on a scale of 1-6 and vascular brown index (VBI) scoring on a scale of 1-4. Morphological and agronomical markers were evaluated and used to group similar lines through cluster analysis. There were significant variations on most of the morphological and agronomical traits. Significant variations in disease severity and the vascular brown index were observed for the cotton lines produced in the half diallel mating system. The general combining ability (GCA) for the parents and specific combining ability (SCA) for the crosses were also significant. The Verticillium wilt severity scores ranged from 1.22 to 3.07 and VBI scores ranged from 0.78 to 2.77. The contribution of GCA to the total sum of squares of crosses for disease scores ranged from 86.9 to 95.2 % compared to SCA that ranged from 4.8 to 14.2 %. Additive gene effects were more important than non-additive effects indicating that Verticillium wilt resistance is genetically determined and that selection should be successful to improve resistance. Selection of parents with good GCA effects will be important for success in Verticillium wilt resistance breeding in cotton.

Germination performance and β-1.3-glucanase expression of tobacco (nocotiana tabacum L) seeds to after-ripening temperature, dry heat treatment and imbibition solutions

Mudzengi, Tashinga Donemore — 2014-11-01T00:00:00Z

Title: Germination performance and β-1.3-glucanase expression of tobacco (nocotiana tabacum L) seeds to after-ripening temperature, dry heat treatment and imbibition solutions Authors: Mudzengi, Tashinga Donemore Abstract: Erratic seed germination is one of the major challenges affecting tobacco production and adoption of improved varieties. This problem can be attributed to seed dormancy and environmental conditions. After-ripening is one of the pragmatic approaches used to enhance the germination of freshly harvested tobacco seeds however the process of after-ripening is a slow and there is need to explore other approaches such as imbibition in phyto-hormones (gibberellic acid and benzyl adenine), imbibition in hydrogen peroxide and dry heat treatment. The aim of the study was to determine the effect of after-ripening temperature, dry heat treatment and imbibition solutions on germination performance and β-1.3-glucanase expression of two selected new tobacco varieties viz KRK 26 R and T71. In the first experiment the effect of after-ripening temperature and imbibition solution effect on tobacco seed germination performance under four different germination environments (20 oC light, 20 oC dark, 30 oC light and 30 oC dark) was evaluated. This first experiment was a 2 x 4 factorial experiment in a completely randomised design with after-ripening temperature at two levels (5 oC and 30 oC) and imbibition solution in four levels (benzyl adenine, distilled water, gibberellic acid and hydrogen peroxide). Freshly harvested seeds were sampled from the two after-ripening temperatures every two weeks for eight weeks and imbibed in the four respective imbibition solutions. In the second experiment the effect of after- ripening temperature and imbibition solution on β-1, 3-glucanase activity in T71 and KRK 26 R incubated under 30 oC light and 30 oC dark was determined using the similar design as the first experiment. The enzyme activity of seeds stored for eight weeks at the two respective after ripening temperatures and imbibed in the four solutions was determined using the reducing sugar spectrophotometry method. The objective of the third experiment was to determine the effect of dry heat treatment (DHT) and imbibition solution on tobacco seed germination percentage performance under 30 oC light and 30 oC dark. This third experiment was a 4 x 4 factorial experiment laid out in completely randomised design with DHT done at 37 oC. The DHT had four levels (30 oC after-ripened seed + no DHT, 5 oC after-ripened seed + no DHT, 30 oC after-ripened seed + seven days DHT and 5 oC after-ripened seed + seven days DHT) and imbibition solution had four levels (benzyl adenine, distilled water, gibberellic acid and hydrogen peroxide). In the first experiment after-ripening temperature and imbibition solutions had interaction (P < 0.05) in all the varieties across all the weeks after storage (WAS) except for T71 (at 6 and 8 WAS) and KRK 26 R (2 and 4 WAS) seeds incubated at 20 oC dark. Under 20oC light seeds after-ripened at 30 oC and imbibed in either hydrogen peroxide or water attained the highest germination rate. However using phyto-hormones did not significant improve germination rate except gibberellic acid for T71 seeds at 2 and 8 WAS. The first experiment also showed that gibberellic acid significantly improves germination percentage of the two varieties incubated in 20 oC dark, 30 oC light and 30 oC dark. Under similar conditions seeds after-ripened at 30 oC marginally improves germination regardless of the imbibition solutions. An interaction was noted between imbibition solution and after-ripening in the second experiment (P < 0.05) except for 30 oC dark incubated T71 seeds (P > 0.05). The second experiment showed that β-1,3–glucanase activity is enhanced by exogenous application of gibberellic acid under both 30 oC light and 30 oC dark. The exposure seeds at 30 oC after-ripening temperature marginally enhanced β-1,3–glucanase activity under the similar conditions. An interaction was attested between DHT and imbibition solution on germination percentage of seed of the two varieties incubated at 30oC light and 30 oC dark in the third experiment (P<0.05). In the third experiment it was established that that DHT enhances germination percentage of 30 oC light and 30 oC dark incubated seeds

Effect of time and method of paclobutrazol application on growth, quality and yield of potato (solanum tuberosum L.)

Mabvongwe, Ottilia — 2014-01-01T00:00:00Z

Title: Effect of time and method of paclobutrazol application on growth, quality and yield of potato (solanum tuberosum L.) Authors: Mabvongwe, Ottilia Abstract: Potato is one of the most widely grown tuber crop that contribute significantly to human nutrition and food security. Potato is a cool season crop and high temperatures are inhibitory to tuberization resulting in low yields. This is mainly due to production of high levels of gibberellins at high temperatures that promote vegetative growth at the expense of tuberization. The balance of hormones that control tuberization can be managed by using anti-gibberellin synthesis such as paclobutrazol to overcome the inhibitory effect caused by gibberellins. Two experiments were set up in a greenhouse with 60% relative humidity, 34 0C(±3) and 21 0C(±3) day and night temperature respectively at Harare Research Station to investigate the effect of paclobutrazol on growth, yield and quality of potatoes. The first experiment was set up as a 4 x 2 factorial design in a CRD with 3 replications to investigate the effect of time of paclobutrazol application on the growth, yield and quality of potato. The first factor was potato variety and the levels were BP1 and Diamond. The second factor was paclobutrazol application time and the levels were 28 DAP, 35DAP, 42DAP and no paclobutrazol applied (control). Early application of paclobutrazol at 28DAP increased yield and starch content by 108% and 28% respectively compared to the no paclobutrazol treatments. The second experiment was set up as a 4 x 2 factorial design in a CRD with 4 replications to evaluate the effect of method of paclobutrazol application and variety on growth, yield and quality of potato. The first factor was potato variety and the levels were BP1 and Diamond. The second factor was paclobutrazol application method and the levels were drench, foliar and no paclobutrazol applied (control). Regardless of the method of application, paclobutrazol increased yield, grades and tuber starch content of potato but the effect was more in drench applied plots compared to foliar applied treatments. Drench application increased stem diameter and yield by 85% and 120% respectively.

Potential of brassica napus and trichoderma harzianum in control of powdery scab (Spongospora subterranea f.sp.subterranea.) of potato (Solanum tuberosum L.)

Manditsvara, Hilda — 2014-12-01T00:00:00Z

Title: Potential of brassica napus and trichoderma harzianum in control of powdery scab (Spongospora subterranea f.sp.subterranea.) of potato (Solanum tuberosum L.) Authors: Manditsvara, Hilda Abstract: Potato (Solanum tuberosum L.) is one of the most important crops grown in Zimbabwe owing to its nutritional and economic benefits. However, its production is often adversely affected by soilborne fungal pathogens such as Spongospora subterranea f.sp subterranea, the causal agent of powdery scab on potato tubers and the vector of Potato Mop Top Virus. The fungal pathogen forms root galls on roots and lesions on tubers. Brassica crops incorporated in crop rotations or applied as green manures have been associated with reduction in soilborne pathogens. Biological control of soilborne plant pathogens by the addition of antagonistic microorganisms to the soil such as Trichoderma spp. has also been suggested. In this study, two experiments were set up in a glasshouse with 340C (±3) and 210C (±3) day and night temperature respectively at Harare Research Station to determine the efficacy of B. napus and T. harzianumin controllingS. subterranea in potato. The first experiment was a 5 x 3 factorial in a CRD with three replications to investigate the effect of B. napus on the incidence and severity of powdery scab on potato. The first factor was B. napus at 10%, 20%, 30% rates with Mancozeb (positive control) and negative control where no control amendment was added. The second factor was potato variety and the levels were BP1, Diamond and Mondial. B. napus 20% reduced disease incidence by 31%, severity by 37% (root galls) and 67% (tubers). B. napus 20% on Mondial resulted inhigh proportion of 100% and 175% on marketable yield, extra-large and large tubers grade respectively compared to the positive control, Mancozeb on Mondial. The second experiment was a 5 x 3 factorial in a CRD with three replications to assess the effect of T. harzianum on the incidence and severity of powdery scab in potato. The first factor was T. harzianumrates were 1gl-1, 2g l-1 , 3g l-1 at 1 x 107CFUg-1with Mancozeb (positive control) and a negative control were no control amendment was applied. The second factor was potato variety and the levels were BP1, Diamond and Mondial.T. harzianum 1 x 107CFUg-1 2g l-1 reduced disease incidence by 26% and severity by 38% (root galls) and 59% (tubers). T. harzianum 1 x 107CFUg-1 2g l-1 on Mondial resulted in 343 % increase in proportion of extra-large tubers compared with the positive control, Mancozeb on Mondial.