Influence Evaluation Of Citrus Disease,Pests And Fruit Quality Under The Screen-house Cultivation

Screen-house cultivation is one of the most important measures for production of green fruits and vegetables.Citrus Huanglongbing,one of the most destructive disease in citrus production,was mainly vectored by citrus psyllid(ACP,Diaphorina citri Kuwayama).To date,no cure has been reported to prevent and control of HLB.Therefore,block the spread of HLB by ACP become the most important point in management of HLB in field.The Screen-house cultivation of citrus is an effective way to prevent HLB spread by ACP and others plant diseases vectored by insects.In this study,the Screen-house cultivation was applied in citrus orchard located in Huizhou city,Guangdong province.The tree vigor,fruit yield,plant disease and insect pests,fruit quality,the concentration of HLB-associated pathogen “Candidatus Liberibacter asiaticus”(CLas),temperature and humidity were compared between the plants in Screen-house areas and whose in the open-air areas.The Screen-house cultivation can provide scientific basis for citrus planting and the foundation for studying the epidemic regularity of citrus HLB.In addition,screen of the effective agents for inhibition of CLas is still the topical in HLB research.Based on the anti-microbial nature for plant pathogenic bacteria,in this study,the Zhongsenmycin was used in field trial to control HLB.Two concentration gradients of agents combined with both foliar spray and root irrigation were applied.This could be provide a theoretical basis for field control of HLB.The main results were following:1.Through the determination of the tree vigor and yield of healthy and HLB-affected trees in the Screen-house areas and open-air areas,the diameter and surface area of the plant canopy in the Screen-house areas were significantly higher than the open-air areas(P<0.05).And the plant height was significantly higher than that in the open-air areas(P<0.01),while no significant difference was observed in canopy diameter,canopy surface area,and plant height between HLB-affected trees in the Screen-house areas and open-air areas.Although there was no significant difference in citrus yield between the Screen-house areas and the open-air areas(P>0.05),the fruit yield of HLB affected trees in the screen house areas was significantly higher than that in the open-air areas(P<0.01).2.The investigation of diseases and pests in the Screen-house areas and open-air areas revealed that the morbidity and disease index of HLB in the Screen-house areas was smaller than that that in the open-air areas.No ACP was found in the Screen-house areas by the monitoring with the yellow plate method and the knocking method.In addition,the abundance and types of other citrus pests in the screen house area were less than in the open-air areas,but opposite result was observed for beneficial insects.3.Tracing records of temperature and humidity in the Screen-house areas and open-air areas,the monthly average of temperature and humidity,highest temperature,and the average of daily temperature and humidity in the screen house areas were significantly higher than those in the open-air areas.4.The measuring of the internal quality,appearance quality and coloring quality of the fruits in the Screen-house areas and open-air areas revealed that the red value of the fruit peel in the Screen-house areas was significantly smaller than the open-air area(P<0.05)and the hue angle of fruit peel was significantly bigger than it in the open-air area(P<0.05).However,there was no significant difference(P>0.05)in internal quality(vitamin C,soluble solids,acidity,TSS/TA ratio and fruit juice rate),appearance quality(single fruit weight,fruit shape index,pericarp thickness,fruit firmness,pericarp rate and residue rate)and others fruit coloring quality(peel yellow value b,skin color saturation C,peel brightness value L)of the fruit from the Screen-house areas and open-air areas.5.The concentration of CLas in the HLB-affected trees in the Screen-house areas and open-air areas was similar,i.e.decrease in February,March,September,and October,but increase from May to August,and change from November to January.The concentration of CLas increased in Screen-house areas during April but decreased in the open-air areas.6.For the treatment trail of HLB-affected trees by Zhongsenmycin with concentration of 1 g/L and 2 g/L(foliar spray and root irrigation),no inhibiting of CLas was observed.