Effects of chitosan oligosaccharide soaking on germination and physiological metabolism of virus-free test tube taro from Jiangxi Yanshan red bud taro at low temperature

Jiangxi Yanshan red bud taro is one of national geographical indication agricultural products from Yanshan County, Jiangxi Province, China. This type of vegetable is generally propagated asexually through corms. Such long-term cultivation can easily lead to virus accumulation and species degeneration. Cultivation of red bud taro virus-free plantlets can restore its species, enhance its growth potential and disease resistance, and significantly increase its yield and quality. However, some challenges are still remained on the large-scale cultivation in the virus-free seedlings of Jiangxi Yanshan red bud taro, such as relatively weak virus-free seedlings, low survival rates of transplantation and domestication, difficulty in long-distance transportation and cultivation, as well as the long-distance exchange of germplasm. Alternatively, virus-free test tube taro can serve as the virus-free seedlings, due to the stronger stress resistance, easy conservation, convenient transportation, and germplasm exchange. Virus-free test tube taro of Jiangxi Yanshan red bud taro can be produced year-round and can achieve industrial production. Virus-free test tube taro of Jiangxi Yanshan red bud taro is generally sown on sunny days from January to early February. Low temperature can limit its germination, and low temperature stress such as "late spring cold" can cause early sown virus-free test tube taro to grow slowly, have a longer emergence cycle, and in severe cases, cause virus-free test tube taro die, resulting in a lower emergence rate and affecting its yield. This study aims to improve the cold resistance of virus-free test tube taro of Jiangxi Yanshan red bud taro in the sowing period. Plant tissue culture and plant physiology were used to determine the germination and physiological indexes of virus-free test tube taro of Jiangxi Yanshan red bud taro under low temperature after soaking with chitosan oligosaccharides. The results showed that the soaking seeds with 200-250 mg/L chitosan oligosaccharide were significantly promoted the germination of virus-free test tube taro of Jiangxi Yanshan red bud taro under low temperature. When the soaking concentration of chitosan oligosaccharide was 200 mg/L, there was the better accumulation of gibberellin (GA₃), ribosylzeatin (ZR), polyamines (PA), and jasmonic acid (JA), whereas, the less accumulation was observed in the auxin (IAA) and abscisic acid (ABA) in terms of endogenous hormones. In terms of antioxidation, 200 mg/L chitosan oligosaccharide could increase in the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), whereas reduce the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂). In terms of osmotic regulation, there was the better accumulation of soluble sugars (SS), soluble proteins (SP) and proline (Pro) when the soaking concentration of chitosan oligosaccharide was 200 mg/L. In terms of metabolic key enzymes, 200 mg/L chitosan oligosaccharide could increase the activity of lipase (LIP), protease (PR) and α- Amylase (ɑ-AMS) and the content of adenosine triphosphate (ATP) . Therefore, 200 mg/L chitooligosaccharide could regulate the content of endogenous plant hormone and osmoregulation substances, as well as the activities of antioxidant enzymes and key metabolic enzymes in the virus-free test tube taro of Jiangxi Yanshan red bud taro at low temperature, and promote its germination. The finding could provide a strong reference for the cold tolerance of virus-free test tube taro from Jiangxi Yanshan red bud taro. It was of great significance for the early spring cold sowing, taro seed germination, and high-yield harvest of Jiangxi Yanshan red bud taro.