Optimization of sampling and monitoring of vegetative flushing in citrus orchards

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 m 2 ) 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 (E r ) of 25%, whereas by the AUFSD, only five trees were necessary to reach an E r 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 (R 2 > 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.

Vegetative shoot flush dynamics of ‘Pera’ sweet orange on three rootstock cultivars

“…New shoot intensities also varied significantly over time with the greatest number of new shoots developing during late spring and early summer, when there is an increase in temperature and water availability to the trees, just after a period of bud dormancy (Spiegel-Roy and Goldschmidt 1996). Major periods of new shoot emergence in late spring and early summer seasons for young and mature citrus trees were also observed by Oliveira (2017) and Carvalho et al (2020) in SPS, Brazil, Catling (1969 in South Africa, and Hall and Albrigo (2007) in Florida.…”

“…Every 20 days, a squared frame of 50 cm x 50 cm was positioned in the outer surface of the canopy, from 1.5 m to 2.0 m above ground level, and all new shoots present within the frame projection were counted and classified. Eight trees per scion-rootstock combination randomly selected in the field were assessed, with each tree taken as a replication (Carvalho et al 2020). Only trees with a healthy overall appearance were used.…”

Metabolomic analysis elucidates how shade conditions ameliorate the deleterious effects of greening (Huanglongbing) disease in citrus

“…To record the abundance of new shoots, on 6 June 2019, all trees were tagged with plastic ribbon flags. Two shoots were chosen and used to indicate the canopy quadrants – southeast and southwest because the southern‐facing quadrants were more likely to flush (Carvalho et al., 2020). For each quadrant, the scouting area was fixed by using a 50 cm × 50 cm square plastic frame (David and Albrigo, 2007).…”

Huanglongbing incidence, canopy volume, and sprouting dynamics of ‘Valencia’ sweet orange grafted onto 16 rootstocks

“…The assessed area in the canopy was 0.5 m × 0.5 m on each side of the canopy (0.25 m 2 each) using a steel frame with its lower edge positioned 1.5 m above the ground, in which all V 2 to V 4 shoot flushes were counted for being the most attractive stages to D. citri (Cifuentes-Arenas et al 2018). Five trees of each rootstock were randomly selected, and the same trees were used for all assessments, considering an acceptable estimation error (less than 10%) (de Carvalho et al 2020). A total of 22 assessments were carried out between July 2016 and November 2017, when the trees were 6-7 years old, and already bearing fruits, thus representing typical adult citrus trees.…”