Plant parasitic organisms in the rizosphere of apple trees in the Western Cape, with special reference to woolly apple aphid

[摘要] ENGLISH ABSTRACT:Various aspects of the biology and ecology of woolly apple aphid, Eriosomalanigerum, were investigated, including initial galling damage caused by E. lanigerum tothe roots of apple trees, the possible relationship between E. lanigerum and Xiphinema andPratylenchus nematodes and the effectiveness of Biostart 2000® and Furfural® as possiblecontrol agents of E. lanigerum in the orchard.Preliminary root damage by first instar E. lanigerum feeding was characterized bythe mechanical injury of endodermis and parenchyma tissues. Damage by second, third andfourth instar E. lanigerum was similar, but the symptoms were more pronounced. Damagecaused by adults included a pronounced swelling at infected areas of the root. Cell wallshardened until the root was radially strengthened with sclerenchyma tissue and nonconductingxylem vessels while the cuticle expanded greatly through the growth of corklikecambium tissue.There was no direct relationship between the population dynamics of E.lanigerum and those of Xiphinema and Pratylenchus nematodes. The occurrence of E.lanigerum appeared to be seasonal while P. penetrans and Xiphinema numbers fluctuatederratically. Undamaged root nitrogen levels seemed to correspond with the normal rootgrowth cycle. Nitrogen levels from galled roots were significantly lower than those ofundamaged roots, probably due to E. lanigerum feeding. Soils rich in fine sand and claysustained higher populations of E. lanigerum and Xiphinema than sandy soils. The numberof E. lanigerum found in soil samples correlated well with the damage index allocated tothe samples. The numbers of Xiphinema found in soil samples also correlated well with thedamage index allocated to the samples according to suspected Xiphinema damagesymptoms.Both Biostart 2000® and Furfural® were effective as control agents of woolly appleaphid. Furfural'Ï, a chemical waste product of the sugarcane industry, was however not aseffective as Biostart 2000®, a product that includes an activator and three bacterial species,Bacillus laterosporus, B. chitinosporus and B. licheniformis. The bacteria in the Biostart2000® treated pots could replicate themselves under suitable conditions while Furfural®dilutes with each watering. Biostart 2000® is also easier to prepare than Furfural® since thecomponents of Biostart 2000® readily mix to form a paste easily thinned by water, whereasFurfural® is an oily substance that does not easily disperse in water.Root damage was initiated soon after E. lanigerum started feeding, however therewas no apparent relationship between E. lanigerum and the nematode species. The mostpromising, environmentally friendly control measure was Biostart 2000®.

[发布机构] Stellenbosch University