Branching responses to pruning in cocoa

Abstract

The branching pattern of a tree determines the efficiency of light interception and carbon assimilation. Pruning can modify the branching pattern, as a result of changes in physiological and environmental conditions, and ultimately pruning can have major effects on yield. For one of the major tropical tree crops, cocoa (Theobroma cacao), very little is known about branching response to pruning. To address this knowledge gap we performed a pruning experiment on young cocoa trees in Cote d' Ivoire. We applied five treatments: two heading treatments (the removal of the terminal apex or 66% of a branch) and two thinning treatments (the removal of 1 or 2 primary branches) and one unpruned control. The branching pattern of the primary branches was described by the number, position, and length of lateral branches right after pruning, and the same observations were repeated after a cycle of leaf production. The probability of branching and the length of lateral branches along a primary branch, in pruned and unpruned conditions, was analyzed using generalized mixed effect models. In unpruned conditions, the probability of branch presence was higher towards the middle of the primary branches and lower at the extremes. Branch length decreased going from the base to the tip of a primary branch. After one cycle of leaf production, new branches emerged preferentially on the distal section of a branch, but probability of branch emergence was reduced by the presence of other lateral branches. Pruning increased the probability of branch emergence mostly towards the tip of a branch, with heavy heading having the strongest effect. By contrast, heavy thinning increased branch emergence also toward the base of the branch. Our results can be applied to improve formation pruning, as this may trigger branching in different part of the crown, depending on the form of pruning. Our study also assists the development of three-dimensional tree models that could further our understanding of the impact of pruning on cocoa growth and productivity.

Positive selection and relaxed purifying selection contribute to rapid evolution of male-biased genes in a dioecious flowering plant

“…However, our results observed male-biased genes but not male-specific genes that underwent relaxed purifying selection. Second, sex-biased genes are often expressed in few tissues (tissue-biased genes) (Meisel, 2011 ;Tosto et al, 2023 ), resulting in these genes rapidly evolving under positive selection or under relaxed purifying selection due to low pleiotropic constraints (Congrains et al, 2018 ;Whittle et al, 2021 ;Tosto et al, 2023 ). In our results, 343 male-biased genes with faster evolutionary rates relative to female-biased and unbiased genes overlapped with tissue-biased genes in floral buds (27 out of 343, 7.87%) (Fig.…”

“…These findings indicate that a small fraction of male-biased genes may experience adaptive evolution due to sexual selection, driven by male-male competition. Alternatively, relaxed constraints could contribute to the rapid evolutionary rates of sex-biased genes through three key characteristics (Dapper and Wade, 2020 ;Tosto et al, 2023 ). First, sexbiased genes are often expressed solely in reproductive tissues of one sex (e.g., sex-specific genes), particularly in the haploid phase (Immler, 2019 ;Beaudry et al, 2020 ).…”

“…Several species have been observed to exhibit rapid evolutionary rates of sequences on sex chromosomes compared to autosomes, which has been related to the evolutionary theories of fast-X or fast-Z (Hough et al, 2014 ;Wright et al, 2015 ;Charlesworth et al, 2018a ). Furthermore, the quantification of gene expression by bulk RNA-seq technology, relative to single-cell transcriptome analysis, has been shown to potentially obfuscate true signals in the evolution of sex-biased gene expression in complex aggregations of diverse cell types (Darolti and Mank, 2023 ;Tosto et al, 2023 ). However, investigation of these interesting issues related to sexbiased gene evolution in T. pilosa can only be conducted when whole genome sequences become available in the near future.…”

“…Such sexual dimorphisms usually arise from differential expression of genes in both sexes, i.e., sex-biased genes (including sex-specific genes exclusively in one sex) that are located on autosomal chromosomes and sex chromosomes/or sex-determining regions (Ellegren and Parsch, 2007 ;Parsch and Ellegren, 2013 ;Charlesworth, 2018b ). Recently, some studies have begun to explore the strength and impact of evolutionary forces that shape different sexually dimorphic traits through sex-biased gene expression (Mank, 2009 ;Rowe et al, 2018 ;Naqvi et al, 2019 ;Tosto et al, 2023 ). Previous studies revealed that sex-biased gene expressions were associated with the evolution of sexual dimorphisms in many animals, although the extent to which exhibits great variation among taxa, tissues, and development stages (Mank, 2017 ;Hsu et al, 2020 ;Khodursky et al, 2020 ;Lichilin et al, 2021 ;Toubiana et al, 2021 ;Djordjevic et al, 2022 ;Yue et al, 2023 ).…”

Predicting resprouting ofPlatanus×hispanicafollowing branch pruning by means of machine learning

“…Leaf area and light are redistributed after the disturbances, which then affects photosynthetic processes (Balandier et al, 2000). This does not simply mean a decrease in photosynthetic capacities, but involves reallocation of carbon-and other resources among plant organs such as fruits (Kohek et al, 2015;Tosto et al, 2023) and flowers (Grechi et al, 2022). What makes the impact of this disturbance even more complex is timing.…”