Impacts of huanglongbing on fruit yield and quality and on flushing dynamics of Sicilian lemon trees

Abstract

IntroductionThe severe Asian form of huanglongbing (HLB), a vascular disease associated with the phloem-limited bacterium ‘Candidatus Liberibacter asiaticus’, is transmitted by the Asian citrus psyllid (ACP) Diaphorina citri. Disease impacts are known for sweet oranges and acid limes but not lemons.MethodsIn a five-year study (2017–2021) we compared yield and fruit quality between naturally-infected and healthy 5-yr-old trees of Sicilian lemon ‘Femminello’, and shoot phenology on both lemon and ‘Valencia’ orange, both grafted onto ‘Swingle’ citrumelo, grown in southeastern São Paulo State, Brazil. HLB severity (percentage of tree canopy area with HLB symptoms) was assessed every 3–4 months, fruit yield and quality in May (2017 to 2019) or June/July (2020-2021), and vegetative and reproductive shoots fortnightly on 50-cm-long branches. The development of ACP on one-year-old seedlings of five lemon varieties, ‘Tahiti’ acid lime, ‘Valencia’ orange, and orange jasmine was evaluated.ResultsSymptoms increased from 11% in 2017 to 64% in 2021, and a monomolecular model estimated 10 years for symptoms to occupy >90% of the tree canopy. On average, production of trees with symptom on 20%, 50% or 80% of the canopy respectively dropped by 18%, 38%, and 53% compared to healthy trees. Fruits of symptomatic branches of lemons were 4.22% lighter and the number of dropped fruits did not correlate with symptom severity. Flushing on symptomatic branches started earlier by 15 to 55 days as compared to the healthy branches of lemon and orange. On diseased trees, vegetative and reproductive shoots respectively increased by 24.5% and 17.5% on lemon and by 67.2% and 70.6% on sweet orange, but fruit set was reduced by 12.9% and 19.7% on lemon and orange trees, respectively. ACP reproduced similarly on all tested plants.DiscussionThe fast symptom progress, significant yield reduction, and earlier flushing on diseased trees, providing conditions highly favorable for the pathogen to spread, reinforce the need of prompt diseased tree removal and frequent ACP preventive control to manage HLB in lemons as in any other citrus crop.

The greening-causing agent alters the behavioral and electrophysiological responses of the Asian citrus psyllid to a putative sex pheromone

“…We recapitulated these findings by testing acetic acid at 10 µg. In agreement with our previous behavioral measurements 2 , 19 , there was no significant difference between male responses to acetic acid (10 µg source dose) or control. Specifically, 74 of 112 tested males responded and spent 5.1 ± 0.3 min in the 10 µg acetic acid treatment and 4.9 ± 0.3 min in the control field of the arena (P = 0.9349, Wilcoxon test).…”

“…This pathogen parasitizes the phloem and blocks nutrient circulation, thus causing citrus trees to become unproductive 1 . Citrus growers suffer severe losses manifested in reduced fruit quality and production and, ultimately, plant death 2 . It has been demonstrated that CLas induces infected plants to produce an ACP attractant, methyl salicylate 3 , leading to ACP's preference for CLas-infected over healthy plants.…”

The greening-causing agent alters the behavioral and electrophysiological responses of the Asian citrus psyllid to a putative sex pheromone

“…We recapitulated these findings by testing acetic acid at 10 µg. In agreement with our previous behavioral measurements, 19,2 there was no significant difference between male responses to acetic acid (10 µg source dose) or control. Specifically, 74 of Page10 112 tested males responded and spent 5.1 ± 0.3 min in the 10 µg acetic acid treatment and 4.9 ± 0.3 min in the control field of the arena (P = 0.9349, Wilcoxon test).…”

“…Citrus growers suffer severe losses manifested in reduced fruit quality and production and, ultimately, plant death. 2 It has been demonstrated that CLas induces infected plants to produce an ACP attractant, methyl salicylate 3 , leading to ACP’s preference for CLas-infected over healthy plants. ACP feeds on infected plants, but due to diseased plants’ low nutritional value, the psyllids move to healthy plants to complete feeding, thus vectoring the HLB-causing agent 3 from infected to healthy trees.…”

The improvement of the quality and shelf life of sweet orange cv. Red blood at ambient temperature through the application of ginger (Zingiber officinale) extracts

“…The citron fruits typically harvest in November and December, after which they are stored in refrigerated conditions (Adewoyin et al, 2022). Starting in January, the demand for citrus fruits increases, but the quality of the fruit deteriorates over time (Cifuentes et al, 2022). Inadequate storage causes a rapid decline in sugar and ascorbic acid levels.…”