Tree water status influences fruit splitting in Citrus

Abstract

a b s t r a c tFruit splitting or cracking is a major physiological disorder in fruit trees markedly influenced by environmental conditions, but conclusive data still are required to provide a definite explanation and preventive measures. Changes in climatic conditions critically influence fruit splitting incidence. We studied plant-soil-ambient water relations in splitting-prone citrus grown under 4 contrasting environmental conditions (climate type and soil), in Spain and Uruguay, over a six years period. Automatic trunk and fruit diameter measurements (trunk and fruit growth rate and maximum daily trunk shrinkage), which are a tree water status indicator, together with factors modifying the tree and fruit water relationship (temperature, ET, rainfall, soil texture, soil moisture, rootstock and xylem anatomy) were studied and correlated with splitting.A close fruit splitting and soil texture relationship was found, inversely correlated with clay and silt percentages, and positively with those for sand. Under 85%-sand soil conditions, slight changes in soil moisture due to fluctuations in temperature, ET, or rainfall changed trunk and fruit growth rate patterns during few hours and induced splitting. Splitting incidence was higher in trees with larger xylem vessels in the fruit peduncle due to rootstock ('Carrizo' and 'C-35' citrange being higher than 'FA-5', 'Cleopatra' and Poncirus trifoliata). Finally, reducing the frequency of irrigation by half increased midday canopy temperatures (∼5 • C) and splitting (+15%). We conclude that irregularities in the tree water status, due to interactions among soil moisture, rootstock and climatic conditions, leads to a number of substantial changes in fruit growth rate increasing the incidence of fruit splitting.

Impact of diseases and pests on premature fruit drop in sweet orange orchards in São Paulo state citrus belt, Brazil

“…After that, the fruit usually drop due to injury. 77,78 Finally, mechanical damage or removal of fruit from the tree caused by inadequate use of equipment and machinery regularly used to manage the orchards is an important cause of crop loss that is frequently neglected. 79 That is specially the case of the SP citrus belt, where the spacing between tree rows has been reduced in the last years to increase tree density.…”

“…Thus, when it rains abruptly, especially after a period of drought, the pulp develops very quickly, putting pressure on the rind, which eventually breaks. After that, the fruit usually drop due to injury 77,78 . Finally, mechanical damage or removal of fruit from the tree caused by inadequate use of equipment and machinery regularly used to manage the orchards is an important cause of crop loss that is frequently neglected 79 .…”

Pre-Harvest Fruit Splitting of Citrus

“…This is evident in observations on 'Nova' mandarin where some values are less than 10% while others are over 50% (Table 1). Wide xylem vessels in the fruit peduncles were associated with increased incidence of PFS, with such vessels apparently conferred by the rootstock [16]. The average lumen diameter of xylem elements was greater in rootstocks with high root hydraulic conductance [45], which confirmed results of studies on xylem elements where trees on Rough Lemon and 'Carizzo Citrange' had more and larger xylem elements than those on 'Cleopatra mandarin' and 'Sour Orange', with increased xylem capacity positively related to water uptake rates [46].…”

“…Regardless of cultivar, PFS was probably mainly a result of "unstable" (i.e., irregular, fluctuating) tree water status, itself an interaction between soil moisture, rootstock, and climatic factors which caused abrupt changes in fruit growth rate [16,17,43,65]. The role of irrigation is to prevent drought-flood cycles to the extent possible given rainfall patterns when used to manage PFS, and this is facilitated by relatively dryer surface layers with wetter soil deeper [17].…”

“…Of all the environmental factors inducing a thin rind, warm and humid conditions during Stage I of fruit development were most important [3]. High PFS was observed with a "dry spring followed by a wet period in stages II and III", based on the assumption that soil moisture status was the main effect [3,5,6,[8][9][10]16,43].…”