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Tokyo University of Agriculture (2018)

Effect of seed priming with polyethylene glycol on growth, quality and capsaicin concentration of hot pepper under drought conditions (Afghanistan)

MOHAMMAD MUSTAFA HARIS

Titre : Effect of seed priming with polyethylene glycol on growth, quality and capsaicin concentration of hot pepper under drought conditions (Afghanistan)

Auteur : MOHAMMAD MUSTAFA HARIS

Université de soutenance : Tokyo University of Agriculture

Grade : Doctoral Dissertation 2018

Résumé
Capsicum species, popularly known as hot pepper, is a popular vegetable in the world. Hot pepper production worldwide in 2016 was 34.5 million tones with 17.79t ha-1 average (FAO, 2016). In many parts of the world, hot pepper is essentially valued for its pungency, nutrition and pigment contents of the fruits (Tian et al., 2014). Hot pepper is also an important horticultural crop in Afghanistan (Walters and Jha, 2016). It is widely utilized as an additive to many Afghan dishes. Afghanistan people eat fresh pepper as well. Northern provinces in Afghanistan are well known for hot pepper production, mostly being exporting to Pakistan as a fresh and dried product (Walters et al., 2012). However, Afghanistan has been suffering from severe drought stress during the past decade, which affected germination, yield and quality of hot pepper as well as other horticultural crops. One of the short-term and most pragmatic approaches to alleviate drought stress is seed priming. Hence, I studied the effect of seed priming with polyethylene glycol (PEG 6000) on growth, quality and capsaicin concentration of hot pepper under drought conditions throughout seed, seedling and growth stages.

* 1. Effect of Drought Stress on Growth, Quality and Capsaicin Concentration of Hot Pepper (Capsicum annuum) The results show that drought stress significantly retarded the growth and increased the ethylene production rate in comparison with daily irrigated control. Fruits harvested at 36 and 45 days after anthesis (DAA) accumulated higher concentration of glucose, fructose and sucrose in response to moderate and severe stress. In addition, capsaicin and dihydrocapsaicin content in fruits harvested at 36 and 45 DAA also showed a significant increase under severe and moderate stress. The present findings revealed that drought stress might alter the primary and secondary metabolites of hot pepper fruits
* 2. Effect of Seed Priming with Polyethylene glycol (PEG 6000) on Seed Viability, Germination of Hot Pepper (Capsicum annuum) Seed priming with high concentration of PEG (-1.2 and -1.6 MPa) significantly increased the seed viability and improved germination percentage. Higher concentration of PEG priming recorded significantly lower seed electrolyte leakage compared to lower concentration of PEG treatments. The effect of PEG priming can be attributed to the slowly achieved imbibition during hydration process and accelerated water uptake during rehydration process after sowing. The results suggest that seed priming with higher concentration of PEG might alleviate the deterioration in seed vigor, achieving the uniformed germination. The enhancement of root/shoot ratio by higher concentration of PEG treatment can also contribute to the adaptability in drought conditions.
* 3. Effect of Seed Priming with Polyethylene glycol (PEG 6000) on Physiological Response of Hot Pepper (Capsicum annuum) Seedlings under Drought Conditions The results suggest that drought stress significantly increased leaf temperature and decreased stomatal conductance as well as photosynthetic rate in moderate and severe drought stress compared to mild treatment. Seedlings primed with higher concentration of PEG recorded increased photosynthetic rate under mild drought stress in accordance with the lesser degree of wilting. The decreased leaf stomatal size and increased number of stomata in the seedlings primed with higher concentration of PEG under drought stress might compensate the reduced stomatal conductance which both decrease photosynthesis and transpiration.
* 4. Effect of Seed Priming with Polyethylene Glycol (PEG 6000) on Quality and Capsaicin concentration of Hot Pepper (Capsicum annuum) under Drought Condition The results suggest that seed priming with higher concentration of PEG induced ethylene production in fruits harvested at 36 DAA under mild and moderate stress. Fruits harvested at 36 DAA under drought stress with lower concentration of PEG priming produced higher concentration of capsaicin and dihydrocapsaicin compared to higher concentration of PEG priming treatment.

Conclusion
The findings of this research suggest that the possibility of PEG priming with -1.2 MPa and -1.6 MPa treatments to maintain physiological activities of hot pepper under drought conditions, with improvements in seedling growth and fruit quality with rich sugars and capsaicinoids. The technique of seed priming with PEG can be hopefully applicable to the small-scale farmers in Afghanistan

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Page publiée le 22 novembre 2021