Dhanyasree, K
Standardization of grafting for water stress tolerance in Papaya (Carica papaya L.) - Vellayani Department of Fruit Science, College of Agriculture 2025 - 197p.
Ph.D
The study entitled “Standardization of grafting for water stress tolerance in papaya (Carica papaya L.)”was carried out at Department of Fruit Science, College of Agriculture, Vellayani, Thiruvanathapuram, during the period 2020-2023 with the objectives to identify water stress tolerant rootstocks from Carica papaya and Vasconcellea species, hormonal induction of side shoots in papaya variety Red Lady, standardization of grafting techniques using induced side shoots onto water stress tolerant rootstocks and evaluation of these grafts for water stress tolerance. The study was designed in a sequential manner in which the first experiment was to identify water stress tolerant rootstock among the papaya varieties Red Lady, CO-2 and CO-8 and Vasconcellea species, such as V. cauliflora, V. cundinamarcensis and V. goudotiana under water stress conditions, followed by experiment on hormonal induction of lateral shoots on papaya variety Red Lady. In third experiment the grafting was standardized by using all subjected rootstocks and lastly, the combined evaluation of papaya graft with the rootstock that exhibit higher drought tolerance and higher survival rate. The first experiment, six rootstocks were evaluated under varying drought stress and flooding stress conditions. The drought stress treatments (D1- Control (100% FC), D2-75% FC, D3-50% FC, D4-25% FC) were induced by gravimetric method and the flooding stress treatments by submerging each plant along with roots containing bag filled with water (100% of the roots submerged) and it was maintained 0 hours (control), 12 hours, 24 hours or 48 hours on 3rd month. The per cent change in plant height and leaf area were maximum (97.27%, 46.79%) in the control plants of V. cauliflora in all stress levels and the root parameters including fresh and dry root weight, fresh shoot weight, fresh and dry root: shoot ratio was observed to be highest in control plants of V. cauliflora. The physiological parameters such as RWC and chlorophyll content exhibited a notable decline as water stress levels increased, with reductions up-to 50% observed in RWC under extreme stressed plants of Red Lady. The lowest decrease of leaf RWC and chlorophyll content were noted in V. cauliflora (30%, 21.5%) under different drought stress regimes. Highest up-regulation in the superoxide dismutase activity (214.50 mg g-1FW) and proline (22.12 µg-1 DW) content were recorded in V. cauliflora, while the highest catalase activity was recorded in V. cauliflora (264.34 units/min/g FW) and peroxidase activity in V. goudotiana (38.26 units/min/g fw) under extreme drought stress condition. Maximum decrease in transpiration rate (E) under the decreasing field capacities were observed in V. cauliflora (2.60 mmol m-2s-1) and the photosynthesis rate (A) and stomatal conductance (gs) were recorded minimum per cent decrease in V. cauliflora with values of 10.2% and 36.2% respectively. The genotype V. cauliflora was found to accumulate the lowest malondialdehyde content (34.80nmol g-1 FW) at 4th month under 25% filed capacity. The rootstocks under flooding conditions noted the per cent change in plant height (107.44%) as the highest in the control plants of V. goudotiana whereas the leaf area and number of leaves were highest in V. cauliflora. The lowest decrease of leaf RWC and chlorophyll content were noted in V. goudotiana with values of 26.25% and 20.2% under different flooding stress regimes. Highest up-regulation in the superoxide dismutase activity (216.68 mg g-1FW) and catalase activity (263.70 units min-1 g -1 fw) were recorded in V. cauliflora which was statistically similar with V. cundinamarcensis and V. goudotiana while maximum proline (23.38 µg-1 DW) content and peroxidase activity (39.49 units min-1 g -1 fw) were recorded in V. goudotiana exposed to 48hrs of submergence. The maximum per cent decrease in transpiration rate (E) under the different flooding conditions was observed in V. cauliflora (47.57%). The photosynthesis rate (A) was recorded maximum in V. goudotiana with value 18.13 µmolm-2s-1 and stomatal conductance (gs) was higher in controlled plants of Red Lady. The control plant of V. cauliflora was found to accumulate the lowest malondialdehyde content (33.89nmol g-1 FW) at 3rd month of flooding. In second experiment the papaya variety Red Lady were treated with two plant bio regulators, separately and their combinations at different levels viz., (T2) GA3 125 mg/L (T3) GA3 250 mg/L, (T4) GA3 500 mg/L, (T5) BA 125 mg/L (T6) BA 250 mg/L, (T7) BA 500 mg/L, (T8) GA3 125 mg/L + BA 125 mg/L, (T9) GA3 250 mg/L + BA 250 mg/L (T10) GA3 500 mg/L + BA 500 mg/L along with (T1) control. The treatment combinations were tried three times at weekly intervals on field grown papaya plants just after flowering (6 month old). Among the treatments, the combination GA3 500 mg/L + BA 500 mg/L recorded minimum number of days for shoot initiation (3.74) and BA 500mg/L produced a higher number of shoots per plant (32.58 and 38.72) at 15 and 30 days after spraying respectively. Whereas, GA3 250 mg/L + BA 250 mg/L recorded more number of shoots per plant at 45 and 60 days after spray (40.50, 41.43) respectively. The plants sprayed with GA3 250 mg/L + BA 250 mg/L registered the maximum number of graftable shoots of 24.08 at 45 days after spraying. GA3 500mg/L recorded maximum length and girth at 60 (13.29, 4.78) days after spray respectively. Third experiment was undertaken to standardize grafting in papaya with six types of rootstocks at one month and two month old using cleft and side grafting. The early first sprout (15 days) was observed in the treatment of cleft grafting on one month old Red Lady rootstock whereas shoot length, shoot girth, number of leaves and leaf area were recorded highest in cleft grafting of two month old Red Lady rootstock at 60 days after grafting. Highest graft success rate of 72.20% and survival percentage of 66.14% were recorded in treatment with cleft grafting of two month old Red Lady rootstock. Among the wild papayas, the treatment combination, two month old Vasconcelleacauliflora rootstock with cleft grafting exhibited higher success rate (62.29%) and survival rate (56.51%). The physiological parameters such as photosynthetic rate and stomatal conductance were recorded highest Vasconcelleacauliflora rootstock and the same recorded least transpiration rate among the rootstocks. Fourth experiment was conducted with the identified rootstock with ideal grafting combination, ie., papaya graft with two month old rootstock of V. cauliflora grafted by cleft grafting were subjected to water stress condition. The per cent increase in plant height, girth and leaf area showed consistency up-to moderate stress levels (75% FC and 12hrs submergence). The control grafts in both stresses recorded maximum values in root parameters, RWC, chlorophyll content, net photosynthetic rate, transpiration rate, MDA activity than the stressed grafts. High up-regulation of enzyme activity (SOD, catalase and peroxidase) and proline content were recorded in extreme water stressed grafts at 4th month of drought stress experiment while it was higher at 3rd month in flooded regimes. In conclusion, amongst the papaya genotypes screened Vasconcelleacauliflora tolerated drought condition of 50% field capacity up-to 6th Month and V. goudotiana and V. cauliflora tolerate flooding stress of 12 and 24hrs of submergence. The best combination for lateral shoots development in papaya var. Red Lady is GA3 250 mg/L + BA 250 mg/L and papaya varieties out-performed the species Vasconcellea with 2 month old rootstock by cleft grafting. Lastly, the cleft grafted plant with two-month old rootstock of V. cauliflora showcased better tolerance of drought and flooding with 75 % field capacity and 12hrs of submergence respectively. Further studies should be conducted to identify the genes/markers for drought and flooding tolerance using molecular techniques and optimization in grafting technique with different rootstocks and grafting conditions.
Fruit Science
Papaya
Carica papaya L.
Grafting
Water stress
634.1 / DHA/ST Ph.D
Standardization of grafting for water stress tolerance in Papaya (Carica papaya L.) - Vellayani Department of Fruit Science, College of Agriculture 2025 - 197p.
Ph.D
The study entitled “Standardization of grafting for water stress tolerance in papaya (Carica papaya L.)”was carried out at Department of Fruit Science, College of Agriculture, Vellayani, Thiruvanathapuram, during the period 2020-2023 with the objectives to identify water stress tolerant rootstocks from Carica papaya and Vasconcellea species, hormonal induction of side shoots in papaya variety Red Lady, standardization of grafting techniques using induced side shoots onto water stress tolerant rootstocks and evaluation of these grafts for water stress tolerance. The study was designed in a sequential manner in which the first experiment was to identify water stress tolerant rootstock among the papaya varieties Red Lady, CO-2 and CO-8 and Vasconcellea species, such as V. cauliflora, V. cundinamarcensis and V. goudotiana under water stress conditions, followed by experiment on hormonal induction of lateral shoots on papaya variety Red Lady. In third experiment the grafting was standardized by using all subjected rootstocks and lastly, the combined evaluation of papaya graft with the rootstock that exhibit higher drought tolerance and higher survival rate. The first experiment, six rootstocks were evaluated under varying drought stress and flooding stress conditions. The drought stress treatments (D1- Control (100% FC), D2-75% FC, D3-50% FC, D4-25% FC) were induced by gravimetric method and the flooding stress treatments by submerging each plant along with roots containing bag filled with water (100% of the roots submerged) and it was maintained 0 hours (control), 12 hours, 24 hours or 48 hours on 3rd month. The per cent change in plant height and leaf area were maximum (97.27%, 46.79%) in the control plants of V. cauliflora in all stress levels and the root parameters including fresh and dry root weight, fresh shoot weight, fresh and dry root: shoot ratio was observed to be highest in control plants of V. cauliflora. The physiological parameters such as RWC and chlorophyll content exhibited a notable decline as water stress levels increased, with reductions up-to 50% observed in RWC under extreme stressed plants of Red Lady. The lowest decrease of leaf RWC and chlorophyll content were noted in V. cauliflora (30%, 21.5%) under different drought stress regimes. Highest up-regulation in the superoxide dismutase activity (214.50 mg g-1FW) and proline (22.12 µg-1 DW) content were recorded in V. cauliflora, while the highest catalase activity was recorded in V. cauliflora (264.34 units/min/g FW) and peroxidase activity in V. goudotiana (38.26 units/min/g fw) under extreme drought stress condition. Maximum decrease in transpiration rate (E) under the decreasing field capacities were observed in V. cauliflora (2.60 mmol m-2s-1) and the photosynthesis rate (A) and stomatal conductance (gs) were recorded minimum per cent decrease in V. cauliflora with values of 10.2% and 36.2% respectively. The genotype V. cauliflora was found to accumulate the lowest malondialdehyde content (34.80nmol g-1 FW) at 4th month under 25% filed capacity. The rootstocks under flooding conditions noted the per cent change in plant height (107.44%) as the highest in the control plants of V. goudotiana whereas the leaf area and number of leaves were highest in V. cauliflora. The lowest decrease of leaf RWC and chlorophyll content were noted in V. goudotiana with values of 26.25% and 20.2% under different flooding stress regimes. Highest up-regulation in the superoxide dismutase activity (216.68 mg g-1FW) and catalase activity (263.70 units min-1 g -1 fw) were recorded in V. cauliflora which was statistically similar with V. cundinamarcensis and V. goudotiana while maximum proline (23.38 µg-1 DW) content and peroxidase activity (39.49 units min-1 g -1 fw) were recorded in V. goudotiana exposed to 48hrs of submergence. The maximum per cent decrease in transpiration rate (E) under the different flooding conditions was observed in V. cauliflora (47.57%). The photosynthesis rate (A) was recorded maximum in V. goudotiana with value 18.13 µmolm-2s-1 and stomatal conductance (gs) was higher in controlled plants of Red Lady. The control plant of V. cauliflora was found to accumulate the lowest malondialdehyde content (33.89nmol g-1 FW) at 3rd month of flooding. In second experiment the papaya variety Red Lady were treated with two plant bio regulators, separately and their combinations at different levels viz., (T2) GA3 125 mg/L (T3) GA3 250 mg/L, (T4) GA3 500 mg/L, (T5) BA 125 mg/L (T6) BA 250 mg/L, (T7) BA 500 mg/L, (T8) GA3 125 mg/L + BA 125 mg/L, (T9) GA3 250 mg/L + BA 250 mg/L (T10) GA3 500 mg/L + BA 500 mg/L along with (T1) control. The treatment combinations were tried three times at weekly intervals on field grown papaya plants just after flowering (6 month old). Among the treatments, the combination GA3 500 mg/L + BA 500 mg/L recorded minimum number of days for shoot initiation (3.74) and BA 500mg/L produced a higher number of shoots per plant (32.58 and 38.72) at 15 and 30 days after spraying respectively. Whereas, GA3 250 mg/L + BA 250 mg/L recorded more number of shoots per plant at 45 and 60 days after spray (40.50, 41.43) respectively. The plants sprayed with GA3 250 mg/L + BA 250 mg/L registered the maximum number of graftable shoots of 24.08 at 45 days after spraying. GA3 500mg/L recorded maximum length and girth at 60 (13.29, 4.78) days after spray respectively. Third experiment was undertaken to standardize grafting in papaya with six types of rootstocks at one month and two month old using cleft and side grafting. The early first sprout (15 days) was observed in the treatment of cleft grafting on one month old Red Lady rootstock whereas shoot length, shoot girth, number of leaves and leaf area were recorded highest in cleft grafting of two month old Red Lady rootstock at 60 days after grafting. Highest graft success rate of 72.20% and survival percentage of 66.14% were recorded in treatment with cleft grafting of two month old Red Lady rootstock. Among the wild papayas, the treatment combination, two month old Vasconcelleacauliflora rootstock with cleft grafting exhibited higher success rate (62.29%) and survival rate (56.51%). The physiological parameters such as photosynthetic rate and stomatal conductance were recorded highest Vasconcelleacauliflora rootstock and the same recorded least transpiration rate among the rootstocks. Fourth experiment was conducted with the identified rootstock with ideal grafting combination, ie., papaya graft with two month old rootstock of V. cauliflora grafted by cleft grafting were subjected to water stress condition. The per cent increase in plant height, girth and leaf area showed consistency up-to moderate stress levels (75% FC and 12hrs submergence). The control grafts in both stresses recorded maximum values in root parameters, RWC, chlorophyll content, net photosynthetic rate, transpiration rate, MDA activity than the stressed grafts. High up-regulation of enzyme activity (SOD, catalase and peroxidase) and proline content were recorded in extreme water stressed grafts at 4th month of drought stress experiment while it was higher at 3rd month in flooded regimes. In conclusion, amongst the papaya genotypes screened Vasconcelleacauliflora tolerated drought condition of 50% field capacity up-to 6th Month and V. goudotiana and V. cauliflora tolerate flooding stress of 12 and 24hrs of submergence. The best combination for lateral shoots development in papaya var. Red Lady is GA3 250 mg/L + BA 250 mg/L and papaya varieties out-performed the species Vasconcellea with 2 month old rootstock by cleft grafting. Lastly, the cleft grafted plant with two-month old rootstock of V. cauliflora showcased better tolerance of drought and flooding with 75 % field capacity and 12hrs of submergence respectively. Further studies should be conducted to identify the genes/markers for drought and flooding tolerance using molecular techniques and optimization in grafting technique with different rootstocks and grafting conditions.
Fruit Science
Papaya
Carica papaya L.
Grafting
Water stress
634.1 / DHA/ST Ph.D