Mechanism Of Physical Resistance To Thrips In Alfalfa (Medicago Sativa L.)

Alfalfa(Medicago sativa L.)plays an essential role in optimizing the agricultural production structure and improving economic efficiency.However,thrips(Thysanoptera:Thripidae)usually results in decreased plant nutrients and groth,low yields,and plant death,which severely limits alfalfa industrial development.Plants can defend against insect infestations chemically and physically.To elucidate the regulation mechanism of physical defense in this superior thrips resistant variety,q RT-PCR technology,cell wall components,epidermal wax,glandular trichomes and non-glandular trichomes were indepth analyzed in‘Caoyuan No.4’(thrips-resistant alfalfa accession)and‘Caoyuan No.2’(thrips-susceptible alfalfa accession)alfalfa varieties.The following conclusions are obtained:1.The insect situation index of ‘Caoyuan No.4’ was lower than ‘Caoyuan No.2’.The phloem of the stem of ‘Caoyuan No.4’ narrows to both sides,the phloem of the main vein vascular bundle of the leaf narrows,and the number of layers of the fence tissue increases;the content of cellulose,hemicellulose,lignin and silicon in the cell wall components of the stem and leaf is high;the waxy leaf epidermis is densely packed throughout the leaf and is evenly distributed;the epidermal hair of the stem and leaf is short,thick,hard and dense,and the angle between the surface of the stem and leaf is greater than 30°,and the physical structure of the leaf stomatal is conducive to protecting its own tissue and reducing the harm of thrips.2.The resistance thrips mechanism of the surface metabolites of ‘Caoyuan No.4’in the grassland is that the total amount of waxy material in the stem epidermis is large,the content of phenols,esters and alcohols in the waxy metabolites of the stem epidermis is high,and there are many alcohol compounds in the glandular hair secretion,which can react with digestive proteins in insects to produce toxic effects and achieve defensive effects.3.The relative expression of related genes found in q RT-PCR analysis is the same as the corresponding physical structure change trend.Therefore,it is speculated that in the anti-thrips alfalfa cultivar ‘Caoyuan No.4’ wax synthetic genes WSD1,FAR,lignin synthesis genes PAL,CAD,silicon synthesis gene Lsi2,pectin synthesis gene GALS1(rhamnosacacturonate glycosalic acid glycosase I synthase),ARAD1(rhamnosacolibid oligosacuretic glycosase I synthase),QUA2(homotypic galacturonic acid glycan synthase),cellulose synthase Ces A3,hemicellulose synthase TBL1,CSLA2 and CSLD2 play an important role in the physical defense response resistance thrips.