Research
Less water , sweeter fruit
By Jenny Ekman
Mild water deficit produces fruit consumers like best , study finds .
Water shortages are most critical when they occur during the final stage of fruit development . At this time accumulation of water drives fruit expansion and , therefore , growth and yield .
If fruit are full of water , the concentrations of sugars and flavor compounds may be reduced . Conversely , sugars – measured as soluble solids ( SSC ) – can increase if trees are slightly water stressed .
However , some studies have found that increased SSC doesn ’ t mean consumers will like them more . For example , even though water stressed Ryan Sun peaches had 5 % higher SSC than normal peaches , consumers didn ’ t like them as much 1 . The researchers suggested this was because they seemed sourer , less juicy and had unappealing texture .
However , a new study just published by Spanish researchers 2 suggests that it is the degree of water stress that is important . They examined the effect of different levels of water stress before harvest on both yield and consumer liking of nectarines . Trees received either :
●● Full irrigation right until harvest ( control )
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Full irrigation until 9 days before harvest , then no irrigation . ( mild deficit )
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Full irrigation until 15 days before harvest then 15 % of normal irrigation volume ( moderate deficit ) Water status in the plant can be assessed using leaf water potential ( LWP ). This is a measure of the force required to extract water from a leaf . If the leaf is fully hydrated ( as when beads of water form ), no pressure is needed and LWP = 0 MPa . If the leaf is wilting , a strong vacuum is needed , so LWP may equal -2.0 MPa or less .
Previous research has shown that expansion of maturing nectarines is reduced if LWP falls below approximately -1.3 to -1.7 at midday 3 . For well-irrigated nectarine trees , LWP at midday generally ranges from -1.0 to -0.5 MPa , depending
12 Australian Stonefruit Grower | December 2016 summerfruit . com . au