Biochemical mechanisms preventing wilting under grafting: a case study on pumpkin rootstock grafting to wax gourd

Houlong Fu; Junyu Fu; Bin Zhou; Haolong Wu; Daolong Liao; Zifan Liu

doi:10.3389/fpls.2024.1331698

Biochemical mechanisms preventing wilting under grafting: a case study on pumpkin rootstock grafting to wax gourd

Front Plant Sci. 2024 May 2:15:1331698. doi: 10.3389/fpls.2024.1331698. eCollection 2024.

Authors

Houlong Fu^#¹, Junyu Fu^#¹, Bin Zhou^{1

2}, Haolong Wu¹, Daolong Liao³, Zifan Liu¹

Affiliations

¹ School of Tropical Agriculture and Forestry, Hainan University, Haikou, China.
² Tropical Crops Genetic Resources Institute, Chinese Academy of Tropical Agricultural Sciences, Haikou, China.
³ Institute of Vegetables, Hainan Academy of Agricultural Sciences, Haikou, China.

^# Contributed equally.

Abstract

Wax gourd wilt is a devastating fungal disease caused by a specialized form of Fusarium oxysporum Schl. f. sp. benincasae (FOB), which severely restricts the development of the wax gourd industry. Resistant rootstock pumpkin grafting is often used to prevent and control wax gourd wilt. The "Haizhan 1" pumpkin has the characteristic of high resistance to wilt, but the mechanism through which grafted pumpkin rootstock plants acquire resistance to wax gourd wilt is still poorly understood. In this study, grafted wax gourd (GW) and self-grafted wax gourd (SW) were cultured at three concentrations [2.8 × 10⁶ Colony Forming Units (CFU)·g^-1, 8.0 × 10⁵ CFU·g^-1, and 4.0 × 10⁵ CFU·g^-1, expressed by H, M, and L]. Three culture times (6 dpi, 10 dpi, and 13 dpi) were used to observe the incidence of wilt disease in the wax gourd and the number of F. oxysporum spores in different parts of the soil and plants. Moreover, the physiological indices of the roots of plants at 5 dpi, 9 dpi, and 12 dpi in soil supplemented with M (8.0 × 10⁵ CFU·g^-1) were determined. No wilt symptoms in GW. Wilt symptoms in SW were exacerbated by the amount of FOB in the inoculated soil and culture time. At any culture time, the amount of FOB in the GW soil under the three treatments was greater than that in the roots. However, for the SW treatments, at 10 dpi and 13 dpi, the amount of FOB in the soil was lower than that in the roots. The total phenol (TP) and lignin (LIG) contents and polyphenol oxidase (PPO) and chitinase (CHI) activities were significantly increased in the GW_M roots. The activities of phenylalanine ammonia lyase (PAL) and peroxidase (POD) initially decreased but then increased in the GW_M roots. When the TP content decreased significantly, the LIG content and PAL and CHI activities increased initially but then decreased, whereas the PPO and POD activities did not change significantly in the SW_M roots. The results indicated that the roots of the "Haizhan 1" pumpkin stock plants initiated a self-defense response after being infected with FOB, and the activities of PPO, POD, PAL, and CHI increased, and additional LIG and TP accumulated, which could effectively prevent FOB infection.

Keywords: Fusarium oxysporum; grafting; pathogenic fungi; plant enzymes; secondary metabolites; wax gourd.

Grants and funding

The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. This research was supported by the National Natural Science Foundation of China (32260752), the National Key Research and Development Program of China (2023YFD1901303) and Central Public Interest Scientific Institution Basal Research Fund (1630032023010, Tropical Crops Genetic Resources Institute, CATAS).