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20233
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Subject: Fruit Science × End date: 2023 × Start date: 2023 × Type: Thesis × Thesis Type: Ph.D ×
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    Mapping of Phytophthora resistance in intergeneric rootstock population of citrus
    (Punjab Agricultural University, 2023) Amandeep Kaur; Sidhu, Gurupkar Singh
    The investigations entitled “Mapping of Phytophthora resistance in intergeneric rootstock population of citrus” were carried out in 2020-22. In the present study, screening of Phytophthora related traits of 88 F1 hybrids population (pseudo-testcross) of Rough lemon × Swingle citrumelo was done by spore suspension and filter method. Data were recorded after 90 days of inoculation for different symptoms and growth attributes related to Phytophthora. Phenotypic characterization for qualitative and quantitative characters of F1 hybrids were done based on IPGRI descriptor. Hybrids were showed great variation in percentage of unifoliate, bifoliate and trifoliate leaves, spine length, habitus, branch size, shoot tip colour, young leaf colour, adaxial colour, abaxial colour, leaf lamina shape, leaf apex, leaf margin and petiole colour. Based on the studied 14 attributes, 88 F1 rootstock hybrids revealed different degree of response to Phytophthora. Out of 14 traits, feeder root rot rating, chlorotic leaves and gummosis rating scale (0 to 4), 23 plants were highly susceptible, 19 plants susceptible, 6 plants moderately resistant, 12 plant resistant and 28 plants in highly resistant. In vitro filter method, lesion size was used to find the degree of resistance and observed that 20 were highly susceptible, 19 susceptible, 12 moderately resistant, 13 resistant and 24 in highly resistant. For genotyping, 165 SSR markers were used for parental polymorphism. Further, a genetic linkage map of citrus F1 hybrids has been constructed by using 116 polymorphic SSR markers comprising of 9 linkage groups, spanning a distance of 1476.19 cM. From the identified, twenty six major Quantitative trait loci (QTL), two QTLs for feeder root rot rating observed on chromosome 2 at 32.54 cM and 14.26 cM having Left flanking marker HvSSRCM-241. A total of 2 QTLs (qGR.RL.pau-5 and qGR.RL.pau-8) for gummosis rating were detected on LG5 & LG8. The proportion of the total variation (R2) ranged from 10.98 to 14.52%, respectively. Third experiment was conducted for mass multiplication and conservation of potential hybrids through cutting. Different types of cutting viz., soft, medium and hard wood cuttings from unifoliate and multifoliate hybrids in rainy and spring season were treated with 500, 1000, 1500, 2000 ppm IBA along with control. Among the cutting taken, medium wood cutting during rainy season and spring season in unifoliate performed better in all the parameters whereas during spring season hardwood cutting of multifoliate hybrids performed better. IBA concentration @ 1000 ppm followed by 500 ppm was the best concentration for all the parameters. Overall, the unifoliate hybrids RL×SW-19 & RL×SW-29 and multifoliate hybrids RL×SW-6 & RL×SW-7 were performed better for all the parameters. The phenotypic linkage so constructed will pave the path for high resolution mapping of Phytophthora resistance traits with high throughput marker segregation techniques like genotyping by sequencing on citrus genetic map. Cutting propagation will provide new insights for future mass multiplication from the limited material.
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    Physiological and anatomical alterations in wilting of guava (Psidium guajava L.) trees and its amelioration using ethylene inhibitor
    (Punjab Agricultural University, 2023) Naik, Eslavath Khamdar; Brar, J.S.
    The guava wilt disease is the foremost threat for guava cultivation not only in India, but also in all major guava growing countries. Hence; the present investigation was planned to get definite information on physiological, anatomical and biochemical aspects involved in this malady so that the consequent amelioration strategies may reoriented. In the present investigations, the comparative analysis of wilt affected and healthy plants were carried out over the developmental period and found significant alterations in physiological, anatomical, biochemical characteristics. Complete mortality of wilt affected trees was recorded within six months of symptoms development at all three locations. With the objective of amelioration strategy, CoCl2 with was sprayed at varied concentrations {0: ppm (wilted control), T2: 50 ppm, T3: 100 ppm, T4 :150 ppm and T5: water spray (healthy control)} at three distinct locations (L1, L2, L3). The treatments of CoCl2, resulted stability with respect to biochemical and physiological changes in plants during initial days and plants were able to survive and consequent improvement all the parameters was observed with the onset of spring season and new flush. Among all treatments CoCl2 @ 150 ppm was more effective for increasing leaf area index, leaf density, leaf thickness, ascorbic acid, leaf water content, though the lower concentration of 50 and 100 ppm were found effective. To confirm the pathogenicity in guava wilt disease, two-year-old guava plants, planted in 26-inch cemented pots were subjected to repeated fungal inoculation (Fusarium solani) with and without stem as well as root injuries singly and in combinations. The results revealed that the fungal inoculations in the rootzone of the plants could not affect the plants, whereas, the inoculation along with root and root+stem injury resulted about 90 % mortality of plants, which was again confirmed by isolating the culture from the shoot tips of the plants. Similarly, in our last experiment, 90 experimental trees exhibiting wilt symptoms were tagged and subjected to different treatments to assess the physiological, anatomical, biochemical, nutritional, fruit yield and quality parameters. The observations recorded on 0, 30, 90, 180 and 300 days revealed significant improvement in plant growth and developments after 90 days of application and values rises significantly the end of observation period (180 to 300 days) and plants resumed the growth as normal. Among all treatments, T4 (150 ppm @CoCl2) followed by T3 (100 ppm @ CoCl2) and T2 (50 ppm @ CoCl2) gave promising results for pigment levels, photosynthetic rate, canopy volume, leaf area index, leaf density and root density. Biochemically, maximum improvement in treated trees was recorded after 180 days of treatments. Data on ethylene and auxin exhibited significant rise in the excised leaves of both wilted and healthy plants initially followed by decline after 8 hours, but at faster rate in wilted plants. From the investigations, it may be inferred that the pathogens are not a primary cause of guava wilt disease. The mechanical root injury or other abiotic stress factors acts as a primary cause to makes the plants prone to be attacked by the pathogen infections. Triggered ethylene level and consequent amelioration of wilting plants using ethylene inhibitor corroborated the hypothesis of investigations.
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    Biochemical characterization and gene expression analysis of pulp pigmentation specific genes in pummelo
    (Punjab Agricultural University, Ludhiana, 2023) Mandeep Kaur; Rattanpal, H.S.
    The present study aimed at morphological and biochemical characterization of pummelo genotypes grown under the subtropical condition of North India along with gene expression analysis for pulp colour developmental genes involved in carotenoid biosynthesis. Morphological characters of pummelo genotypes were studied as per International Plant Genetic Resources Institute, Italy descriptors for citrus. A wide range of genetic diversity was observed for fruit length (102.1-158.6 mm), fruit diameter (98.8-146.7 mm), peel thickness (10.9-21.8 mm), fruit weight (427.2-1150.0 g), peel weight (179.7-526.2 g), juice content (76.6-221.3 ml) and seed number per fruit (51.0-132.0) whereas, a relatively narrow range of genetic diversity was observed for flower length (30.0-41.4 mm), number of petals (4-5) and the number of segments (15.0-20.0). The highest fruit size was recorded in NRCC Pummelo5 and PTF-1. Basic fruit quality attributes and components of the antioxidant defense mechanism were estimated colorimetrically. Among biochemical attributes (total soluble sugars, titratable acidity, total sugars, sucrose and reducing sugars), NRCC Pummelo-3 and PTF-4 had the best quality fruits on account of the maximum sugar-acid ratio. Relatively higher content of vitamin C, total phenols, total flavonoids, o-dihydroxy phenols and total antioxidant capacity (DPPH and activity of antioxidant enzymes - superoxide dismutase, catalase, ascorbate peroxidase and peroxidase) was recorded in PTF-4 and NRCC Pummelo3. With respect to the volatile composition of pummelo genotypes as determined by GC-MS analysis, a total of thirty and sixty one volatile compounds were identified in pummelo peel oil and juice, respectively. Limonene was observed as the most predominant compound in pummelo peel oil as well as juice. Additionally, the expression of pulp pigmentation-specific genes in pummelo genotypes including pink-fleshed (NRCC Pummelo-3 and PTF-4) and white-fleshed (Local) was studied. The genes upstream of the lycopene biosynthesis (HDS, HDR, DXS, DXR, PDS, PSY, ZDS, ZISO, CRTISO and PLIS) were up-regulated whereas the genes downstream of the lycopene biosynthesis (ε-LCY, ε-CHX, β-CHX, CCD1, CCD4, AAO3, A1CYP707, A3CYP707 and A4CYP707) were down-regulated. Relative expression of carotenoid biosynthesis genes was the highest in NRCC Pummelo-3 than PTF-4 with respect to Local genotype. The information generated may assist fruit breeders to shortlist the genotypes in hybridization programs for the development of nutritionally-enriched cultivars.