ACP nymphs preferred to settle and feed on the lower (abaxial side of young leaves either on secondary veins or on the sides of the midrib, whereas adults preferred to settle and feed on the upper (adaxial or lower secondary veins of young or old leaves. Stylet morphometrics of ACP nymphs and adults were studied in relation to citrus vein structure and to their putative (histologically verified feeding sites on Valencia orange leaves. Stylet morphometrics and citrus leaf vein structure in relation to feeding behavior of the Asian citrus psyllid Diaphorina citri, vector of citrus huanglongbing bacterium.ĭirectory of Open Access Journals (Sweden)įull Text Available The Asian citrus psyllid (ACP, Diaphorina citri (Hemiptera: Psyllidae, is the primary vector of the phloem-limited bacterium Candidatus Liberibacter asiaticus (LAS associated with huanglongbing (HLB, citrus greening, considered the world's most serious disease of citrus. Previous studies indicate that HLB infection causes disorder in the phloem and severely impairs the translocation of assimilates in later changed to Candidatus Liberibacter spp.) in nomenclature (18,25,34). The disease tends to be associated with a phloem-limited fastidious -proteobacterium given a provisional Candidatus status (Candidatus Liberobacter spp. HLB is one of the most devastating diseases of citrus (6,13), characterized by blotchy mottling with green islands on leaves, as well as stunting, fruit decline, and small, lopsided fruits with poor coloration. In recent years, citrus Huanglongbing (HLB), also called citrus greening, has severely affected Florida's citrus production and hence has drawn an enormous amount of attention. Citrus is the most important commercial fruit crop in Florida.
These data implicate Las as the pathogen responsible for HLB disease. The PhyloChip analysis was further verified by sequencing 16S rDNA clone libraries, which indicated the dominance of Las in symptomatic leaves. Candidatus Liberibacter asiaticus (Las) was detected at a very low level in asymptomatic plants, but was over 200 times more abundant in symptomatic plants. PhyloChip arrays indicated that nine taxa were significantly more abundant in symptomatic midribs compared to asymptomatic midribs. PhyloChip analysis indicated that 47 orders of bacteria from 15 phyla were present in the citrus leaf midribs while 20 orders from phyla were observed with the cloning and sequencing method. Our results revealed that citrus leaf midribs can support a diversity of microbes. We employed a combination of high-density phylogenetic 16S rDNA microarray and 16S rDNA clone library sequencing to determine the microbial community composition of symptomatic and asymptomatic citrus midribs. The bacterial diversity associated with citrus leaf midribs was characterized 1 from citrus groves that contained the Huanglongbing (HLB) pathogen, which has yet to be cultivated in vitro. Midrib vein cutting has been suggested to have evolved as a countermeasure to deactivate induced leaf latex or cardenolide defences of milkweeds and dogbanes, yet vein cutting effects on leaf physiology seem more severe than the non- midrib defoliation the defences evolved to deter.īacterial diversity analysis of Huanglongbing pathogen-infected citrus, using PhyloChip and 16S rRNA gene clone library sequencingĮnergy Technology Data Exchange (ETDEWEB) Non- midrib tissue defoliation reduced whole- leaf photosynthetic activity mostly by removing photosynthetically active tissue, while midrib injury was most severe as the injury location came closer to the petiole. The degree of gas exchange impairment from midrib injury was usually more severe than from manually imposed and actual insect defoliation (non- midrib), where partial recovery occurred after 28 d in one milkweed species. Midrib vein injury impaired several leaf gas exchange parameters, but only downstream (distal) from the injury location. Leaf gas exchange response to midrib injury was measured in five Asclepiadaceae (milkweed), one Apocynaceae (dogbane), one Polygonaceae and one Fabaceae species, which have been observed or reported to have midrib vein cutting injury in their habitats. We examined how injury to a leaf's midrib vein impairs gas exchange, whether impairment occurs downstream or upstream from injury, duration of impairment, compared the severity of midrib injury with non- midrib defoliation, and modelled how these two leaf injuries affect whole- leaf photosynthesis. One type of specialised herbivory receiving little study even though its importance has frequently been mentioned is vein cutting. An insect countermeasure impacts plant physiology: midrib vein cutting, defoliation and leaf photosynthesis.
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