Plant Growth Promotion and Biocontrol of Leaf Blight Caused by Nigrospora sphaerica on Passion Fruit by Endophytic Bacillus subtilis Strain GUCC4

Abstract

Passion fruit (Passiflora edulis Sims) is widely cultivated in tropic and sub-tropic regions for the production of fruit, flowers, cosmetics, and for pharmacological applications. Its high economic, nutritional, and medical values elicit the market demand, and the growing areas are rapidly increasing. Leaf blight caused by Nigrospora sphaerica is a new and emerging disease of passion fruit in Guizhou, in southwest China, where the unique karst mountainous landscape and climate conditions are considered potential areas of expansion for passion fruit production. Bacillus species are the most common biocontrol and plant-growth-promotion bacteria (PGPB) resources in agricultural systems. However, little is known about the endophytic existence of Bacillus spp. in the passion fruit phyllosphere as well as their potential as biocontrol agents and PGPB. In this study, 44 endophytic strains were isolated from 15 healthy passion fruit leaves, obtained from Guangxi province, China. Through purification and molecular identification, 42 of the isolates were ascribed to Bacillus species. Their inhibitory activity against N. sphaerica was tested in vitro. Eleven endophytic Bacillus spp. strains inhibited the pathogen by >65%. All of them produced biocontrol- and plant-growth-promotion-related metabolites, including indole-3-acetic acid (IAA), protease, cellulase, phosphatase, and solubilized phosphate. Furthermore, the plant growth promotion traits of the above 11 endophytic Bacillus strains were tested on passion fruit seedlings. One isolate, coded B. subtilis GUCC4, significantly increased passion fruit stem diameter, plant height, leaf length, leaf surface, fresh weight, and dry weight. In addition, B. subtilis GUCC4 reduced the proline content, which indicated its potential to positively regulate passion fruit biochemical properties and resulted in plant growth promotion effects. Finally, the biocontrol efficiencies of B. subtilis GUCC4 against N. sphaerica were determined in vivo under greenhouse conditions. Similarly to the fungicide mancozeb and to a commercial B. subtilis-based biofungicide, B. subtilis GUCC4 significantly reduced disease severity. These results suggest that B. subtilis GUCC4 has great potential as a biological control agent and as PGPB on passion fruit.

Nigrospora oryzae Causing Leaf Spot Disease on Chrysanthemum × morifolium Ramat and Screening of Its Potential Antagonistic Bacteria

“…As a means of prevention and control of plant disease, biological control has been greatly promoted in today’s widespread use of chemical pesticides. Screening microorganisms with biocontrol effects from different parts is a good choice; for example, Wang et al screened many antagonistic Bacillus strains from passion fruit leaves, which can prevent disease caused by N. sphaerica [ 29 ]. In this article, 12 biocontrol strains with antagonistic effects were screened from the leaves of Chrysanthemum morifolium , among which Bacillus siamensis D65 had the most significant antagonistic effect and could be further studied as an effective biocontrol resource.…”

“…The antagonism ability of each antagonistic strain screened from the previous study was determined by dual culture assay on PDA plates [ 29 ]. In general, we took a 6 mm agar–mycelium plug obtained from N. oryzae that had been cultured on PDA medium for 5 days, placed in the center of a new PDA plate, and incubated in the dark conditions of 27 °C for 1 day.…”

Biocontrol potential of endophytic Pseudomonas strain IALR1619 against two Pythium species in cucumber and hydroponic lettuce

“…Excessive nitrogen and a lack of natural antagonistic organisms in hydroponic systems may also be contributing factors to high disease incidence [ 9 ]. The use of biocontrol agents (BCA), including endophytes for disease control is a more sustainable and environmentally friendly alternative to conventional fungicides [ 30 , 31 ]. The Institute for Advance Learning and Research (IALR) maintains a sizeable collection of bacterial endophytes isolated from wild plants (n ≈ 2000).…”

Effects of exogenous zinc on the physiological characteristics and enzyme activities of Passiflora edulis Sims f. edulis seedlings

“…Passiflora edulis Sims is native to Brazil and is distributed in tropical and subtropical regions ( Liu, Tang & Zhou, 2021 ). P. edulis Sims is grown in many places in southern China and the market demand has increased rapidly in recent years ( Wang et al, 2023 ). As one of the main cultivated varieties, P. edulis Sims f .…”

“…As a necessary mineral nutrient element for plants, Zn has an important effect on the growth and physiological functions of crops ( Gupta, Srivastava & Singh, 2023 ). At present, research on the application of Zn fertilizer is mainly aimed at wheat ( Li, Zeng & Su, 2022 ), rice ( Yang et al, 2021 ) and other crops, and research on P. edulis Sims is mainly focused on the prevention and control of viral diseases ( Wang et al, 2023 ), cultivation and breeding ( Phong et al, 2022 ). There are few reports on the application of Zn fertilizer to P. edulis Sims f. edulis seedlings, which is not conducive to the popularization and utilization of Zn fertilizer in the efficient production of P. edulis Sims.…”