Introduction: Papaya (Carica papaya L.) is a plant from the Caricaceae family and grows well in tropical and subtropical regions. Seed Pretreatment and culture substrate are important and effective factors in the processes of germination and seedling growth. In seed priming, seeds are partially hydrated to allow metabolic events to occur without actual germination and then re-dried.
Materials and Methods: The experiment was done in a factorial arrangement with the two factors of seed pretreatment and culture substrate in a completely randomized design with 15 treatments, 3 replications, and 10 seeds per replication. This experiment was conducted in 2022 in the research greenhouse of University of Zabol. Pretreatment of seeds including distilled water as control (P0), humic acid (P1) and seaweed (P2) and culture substrate including compost: perlite: vermicompost (1:1:1) (S1), compost: perlite: cocopeat (1) :1:1) (S2), compost: vermicompost: cocopeat (1:1:1) (S3), perlite: vermicompost: cocopeat (1:1:1) (S4) and compost: perlite: vermicompost: cocopeat (1) :1:1:1) was (S5). Pretreatment of biofertilizers including 200 mg/l of humic acid (Humi grow 80% Gardesco) and 2 g/l of 30% Hortiland Vita free seaweed extract based on Ascophyllum nodosum was used for the pretreatment of Bangladeshi variety papaya seeds. Before planting, seeds were first disinfected with 1% sodium hypochlorite solution for 2 minutes and then rinsed 3 times with distilled water. They were then soaked in the pre-prepared solutions at a temperature of 25 °C for 24 hours in dark room, and then air dried and were cultivated in 32-cells plug containing the desired culture substrates.
Results and Discussion: The results indicated a significant effect of seed pretreatment and culture substrate on the germination and growth of papaya seedlings. The minimum average germination time (11.20 day), maximum germination speed index (0.72), seedling vigor index (2342.49) and root dry weight (0.079 g) were recorded for humic acid pretreatment. In addition, under the influence of biopriming with both humic acid and seaweed biofertilizers, the maximum percentage of germination (81% and 79%, respectively), number of leaves (6.30 and 6.23, respectively) and stem diameter (2.43 and 2.36 mm, respectively) compared to the control. Among the cultivation substrates, S5 and S3 substrates showed better results in terms of germination and seedling growth compared to other cultivation substrates. Examining the results of interaction showed that the maximum seedling height was observed in treatments P1S5 (21.03 cm), P1S3 (20.87 cm), P1S4 (19.99 cm) and P1S2 (19.82 cm). P1S5 and P1S3 treatments recorded the highest root length with a statistical class of 9.73 and 9.46 cm, respectively. The maximum shoot dry weight was recorded for treatments P1S5 (0.319 g), P1S4 (0.309 g) and P2S5 (0.302 g) without statistical difference. The plants obtained from the seeds pretreated with humic acid and grown in the S5 culture substrate had significant shoot and root dry weights; This is due to the rapid reversal of seed dormancy and the beginning of germination, as well as the ease of absorption of more water and nutrients by plants during the growth period.
Conclusion: seed biopriming accelerated the germination process and increased the growth of papaya seedlings. Cultivation substrates containing vermicompost showed significant results for seed germination, establishment and growth of papaya seedlings. Based on the results of the present study, it is recommended to use seed biopriming, especially with humic acid biofertilizer and vermicompost-containing culture substrate, to increase the germination percentage and produce healthy seedlings.