Abstract
Citrus trees produce flushes throughout the year, but there are no criteria established for a precise shoot monitoring in orchards under tropical climate. Methods for quantification of flush dynamics would be useful for horticultural and pest management studies because different insect vectors feed and reproduce on flushes. We estimated the minimum number and distribution of trees for sampling and determined the flushing pattern over time in ‘Valencia Late’ orange trees grafted onto ‘Swingle’ citrumelo rootstock. Shoots within a square frame (0.25 m2) on two sides of the canopy were counted and classified by their phenological stage. The minimum number of samples was estimated using the mean number of shoots and area under the flush shoot dynamics (AUFSD). The temporal and spatial distribution analysis was performed by Taylor’s power law and by multiple correspondence analysis (MCA). Additionally, a shoot maturity index (SMI) based on visual qualitative assessment of flushes is proposed. Considering the mean number of shoots, it was necessary to sample two sides of 16 trees to reach a relative sampling error (Er) of 25%, whereas by the AUFSD, only five trees were necessary to reach an Er of 10%. Flushes were predominantly randomly distributed over time and space. Testing eight transects, sampled trees should be distributed throughout the block, avoiding sampling concentration in a certain area. MCA showed that the west side and the upper sampling positions of trees were more likely to be associated with younger shoots. AUFSD and the evaluation of both sides of the canopy yielded a smaller number of trees to be assessed. The SMI was a reliable metric to estimate the shoot phenology of orange trees, and correlated well (R2 > 70%) with the mean number of shoots within the square frame. Therefore, SMI has the potential to make shoot monitoring in the field more practical.
Highlights
Citrus is among the most important fruit crops in the world and is cultivated under a wide range of climate types [1]
Evaluating the shoot growth of citrus trees is important in studies on crop physiology and production, as well as for germplasm evaluation
This information could improve the criteria for pest management procedures, for instance by the means of determining periods of higher host favorability, since flushes are a main entry way for several pathogens of citrus
Summary
Citrus is among the most important fruit crops in the world and is cultivated under a wide range of climate types [1]. Vegetative growth in citrus trees is affected by environmental factors and occurs in several cycles (flushes) over the year. Estimation of citrus flush patterns can provide useful information for studies on plant physiology and decision making on management of citrus production. Scouting of flushes may contribute to integrated pest management decisions, since new shoots are one of the main entry points of vector-borne pathogens of citrus. Citrus variegated chlorosis (CVC) is caused by Xylella fastidiosa and vectored by several leafhoppers [3]. Citrus canker is caused by Xanthomonas citri subsp. Citri, whose incidence and severity are exacerbated by the damage produced by the citrus leafminer (Phyllocnistis citrella Stainton) [4]. Knowledge about the distribution pattern of the young shoots in different parts of the plant and among different plants of the orchard throughout the seasons is useful for deciding how and when to sample flushes [9]
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