Characteristics Of Root Exudates And Its Reaction To Faba Bean Fusarium Wilt In Wheat And Faba Bean Intercropping

Wheat and faba bean intercropping is a traditional agricultural practice which is widelyadopted by farmers in southwest China. Results from agriculture production and numerous fieldtrials showed that wheat and faba bean intercropping could significantly improve crop yields anddecrease diseases incidence. Characteristics of nutrients uptake, water absorption, carbon andnitrogen metabolisms, dynamic changes of rhizosphere available nutrients and rhizospheremicrobe flora and yield advantages in wheat and fababean intercropping have been stated in manypublications. However, little about the characteristics of root exudates in this intercropping areknown. Root exudates play an important role in rhizhosphere micro-ecological environment andagro ecosystem. In wheat and faba bean intercropping, there are close correlations betweenintercropping and soil nutrients mobilization, growth of rhizosphere microorganisms and soil borndiseases. But the reasons are still unclear. In this studies pot trials and hydroponic cultures ofwheat and faba bean intercropping were carried out, exudates from the roots were collected andexamined by HPLC and chemical analysis to investigate the types and amounts of organic acids,phenolic acids, ammonia acids and sugar during crop different growth stages. Meanwhile,responses of organic acids in root and rhizosphere to fusarium oxysporum infection inintercropping were analyzed. The main results are as follows:(1)Wheat and faba bean intercropping（W//F）were of significantly yield (biomass)advantages. The land equivalent ratio (LER) was1.12and1.04in pot and hydropoinc culturerespectively. W//F increased root/shoot ratio of faba bean in comparison with that of monocropedfaba bean(MF), and both root activity of wheat and faba bean increased in intercropping.Meanwhile, there was increase trend of N and P uptake and accumulation in intercropping duringharvest stage in comparison with that of monocropping. Intercropping also increased N and Ptranslocation from roots to seeds of faba bean.(2) W//F increased total amount of organic acids (OA) in root exudates (RE) in comparisonwith that of monocropping. In pot culture, the total amount of OA in RE of intercroppingwheat(IW) was increased by155%、35.6%and92.6%at tilering, booting and filling stagerespectively in comparison with mono cropping wheat (MW). And total amount of OA in RE ofintercropping faba bean (IF) was increased by87.4%and38.7%at branching and filling stagerespectively in comparison with mono cropping faba bean (MF). In hydroponic culture, the totalamount of organic acids in RE of W//F was1.5times higher than that of MF at flowering stage.(3) W//F changed types of OA in RE in comparison with that of monocropping. In pot culture,lactic and citric acid was detected in RE of IW at tilering and jointing stage of wheat, but that wasnot detected in that of MW. At branching stage of faba bean, acetic acid was detected in RE of IF,wherea lactic acid was detected in RE of MF.At filling stage of faba bean, lactic, acetic and citic acid was detected in RE of IF, whereas acetic, citic and fumaric acidbut was detected in that ofMF.In hydroponic culture, fumaric acid was detected in RE of W//F at booting stages, but that wasnot detected in that of MW. And oxalic, tartaric, citric and fumaric acid was detected in RE ofW//F, but not detected in MF at flowering stage.(4)W//F increased root exudation rate of organic acids in comparison with that of monocropping. In pot culture, exudation rate of citric and fumaric acid of IW was179times and184times higher than that of MW at booting stage respectively. And exudation rate of lactic acid ofIW was2.53times higher than that of MW at filling stage. In hydroponic culture, exudation rateof citric and fumaric acid of IW was4.6times and3.2times higher than that of MW at jointingstage respectively.(5)In comparison with monocropping, W//F decreased total amount and types of phenolicacids (PA) in RE, and declined exudation rate of PA. W//F decreased total amount of phenolicacids(PA) in RE by64.6%、70.01%and39.0%at tilering, jointing and booting stage respectivelyin comparison with that of MW. And W//F decreased total amount of PA in RE by37.5%and57.79%at branching and flowering stage respectively in comparison with that of MF. Exudationrate ofρ-hydrobenzoic，vanillic and syringic acid was decreased in intercropping during thewhole growth stages in comparison with that of MW. Vanillic and ρ-hydrobenzoic acid wasdetected in RE of MF at branching and flowering stage of faba bean, but that was not detected inthat of W//F.PA content of IW rihzosphere decreased in comparison with that of MW, andintercropping changed types of PA in rhizsophere in comoparison with that of MF.(6)Intercropping improved total amount of amino acids (AA) in RE in comparison with thatof monocropping.Total amount of AA in RE of IF was increased by19.6%~75.9%during thewhole growth stages in comparison with that of MF, and total amount of AA in rhizosphere of IFwas1.9times~7.6times higher than that of MF. Meanwhile, W//F significantly increased totalamount of AA in rihzosphere of IW at jointing and booting stages, compared to MW.(7) In comparison with monocropping, W//F increased total amount of sugar in RE. In potculture, total amount of sugar in RE of IW was increased by126.9%，34.9%and59.8%atjointing, booting and filling stage respectively compared to MW. At the same time, sucrosecontent in RE of IW was2.37times,1.41times and2.0times higher than that of MW respectively.In hydropoinc culture, total amount of sugar in RE of W//F was3.16times,2.78times and3.92times higher than that of MF at branching, flowering and booting stage respectively.Meanwhile, both reduce sugar and sucrose content in RE of W//F was higher than that of MF.(8) Fababean fusarium wilt incidence and severity index were decreased in intercropping incomparison with that of monocropping, and total amount of AA in faba bean root and rhizospherewere decreased too in intercropping after Fusarium oxysporum injection. In comparison with MF,intercropping significantly decreased content of citric and malic acid in rhizosphere and resulted in decreasing of fusarium wilt incidence and severity.