The most important problem in world citrus production is the bacterial disease Huanglongbing (HLB; greening) which is caused by a phloem-limited bacterium that is vectored by a phloem-feeding psyllid. The earliest visible symptoms of HLB in leaves are an asymmetrical chlorosis referred to as "blotchy mottle", thought to be from starch accumulation from a phloem dysfunction and a decline in root health. We tested the hypothesis that such visible symptoms are not unique to HLB by stemgirdling two year-old seedling trees of 'Cleopatra' mandarin and 'Swingle' citrumelo rootstocks in the greenhouse. Girdling induced a 4-fold greater starch concentration in leaves on well-watered trees while starch in woody roots of girdled trees decreased up to 19 fold relative to non-girdled trees. Drought stress cycles induced some starch accumulation in non-girdled roots but there were no effects of drought stress on root starch in girdled trees. Girdling reduced leaf transpiration in well-watered trees. Leaves on girdled trees clearly had HLB-like visible blotchy mottle symptoms but no visible symptoms developed on non-girdled trees. The up to 40% increase in leaf starch increased leaf dr wt per leaf area (DW/LA) and consequently reduced many leaf nutrients on a leaf DW basis. Most of these differences disappeared when expressed on a LA basis except for the girdle-induced decreases of leaf phosphorous and sulphur. Leaf boron (B) was inversely related to leaf starch when both were expressed on a LA basis. In the absence of HLB, girdling increased leaf starch, decreased root starch, and duplicated the asymmetric blotchy mottled visual leaf symptoms that have been associated with HLB-infected trees.
|Numero di pagine||7|
|Stato di pubblicazione||Published - 2016|
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