Screening Of Efficient PGPR Strains Of Watermelon And Their Properties In Growth Promotion And Disease Control

Watermelon possessing edible and medicinal value,is a very important economic crop in our country.Fusarium wilt caused by the soil-borne vascular fungal pathogen Fusarium oxysporum f.sp.niveum,is the most destructive disease in watermelon worldwide,causing approximately 30–50% yield losses.Biological control which is greenly,environmentally and efficiently,has become a hotspot for controlling plant diseases.PGPR strains not only have little pollution,high efficiency,improve soil structure,etc.,but also promote crop growth and development,resistance against pathogenic fungi,have great significance for the sustainable development of agriculture.phlD is the key gene to synthesize 2,4-diacetylphloroglucinol,the strain with phlD is considered to have the potential ability to synthesize 2,4-DAPG.This study will screen the functional PGPR strains with the gene phlD by PCR amplification from 30 watermelon PGPR strains,and analyze their growth-promoting characteristics such as production of IAA,siderophore,HCN,ACC deaminase as well as phosphate solubilization.The semi-solid tests,hydroponic experiments and outdoor pot experiments were designed to screen effective functional strains which not only promote the growth of watermelon but also control the watermelon Fusarium wilt.The effective strains provide experimental materials and theoretical basis for the prevention and treatment of Fusarium wilt.The main findings are as following.1.This test screened 15 watermelon PGPR strains with the gene phlD by PCR amplification.2.The growth-promoting properties of 15 strains with the phlD were evaluated.The result showed that all of them could secrete IAA and siderophores,13 of them possessed phosphate solubilization activity,11 of them had the ability of producing hydrogen cyanide,and 3 strains had ACC deaminase activity.10 strains were founded with four kinds of growth-promoting activities,and the strain 2S5 possessed five kinds of growth-promoting activities.3.The 12 indices including main root length,total root length,total surface area,root average diameter,total root volume,total root tips,total forks,total crossings,fresh and dry weight were measured in semi-solid tests and hydroponics experiments.The tests aim to screen the efficient PGPR strains which can obviously promote the growth of watermelon seedlings and roots.The results of semi-solid tests showed that the strain YFRE5,YGRE4 and 2S5 had obvious promoting effects on watermelon seedlings,the three strains respectively possessed 4,6,5 indicators which showed significant addition than the comparison(p < 0.05),included root fresh weight,total root length and total root surface area and other indicators.With the results of semi-solid tests,five strains(Y3,FRBN3,YFRE5,YGRE4 and 2S5)having great growth-promoting effect on watermelon seedlings,were screened and used in the hydroponics experiments.The results of hydroponics experiment showed that the strains FRBN3,YFRE5,YGRE4 and 2S5 have 10 or more indicators showed significant addition than the comparison(p < 0.05),including aerial parts fresh weight,dry weight and root fresh weight,dry weight,total root length,total root surface area,total root volume,total root tips,total forks,total crossings and other indicators.4.Thtree efficient strains FRBN3,YFRE5 and YGRE4 were studied in the outdoor pot control effect test further.The results showed that the three efficient strains had a significant growth-promoting effect on watermelon plants in different degrees.The aerial parts fresh weight of plants inoculated with strains FRBN3 ? YFRE5 and YGRE4 significantly increased by 32%?62% and 35% and the root fresh weight significantly increased by 41%?53% and 25%.The three efficient strains also had a significant control effect on Fusarium wilt,after inoculation of strains FRBN3,YFRE5 and YGRE4,the disease index significantly reduced by 63.8%,70.2% and 64.9%,respectively.The three strains were identified as Pseudomonas sp.,Pseudomonas sp.,Bacillus sp.by the 16 S rDNA sequence analysis and physiological and biochemical characteristics respectively.In summary,the three efficient strains FRBN3,YFRE5 and YGRE4 having multiple growth-promoting activities,showed a significant disease control effect on watermelon plants,and have great potential for control of Fusarium wilt.