Plant Gene and Trait 2024, Vol.15, No.5, 265-274 http://genbreedpublisher.com/index.php/pgt 266 2 Kiwifruit Stress Factors and Their Impact 2.1 Abiotic stresses Kiwifruit is highly sensitive to various abiotic stresses, including drought, salinity, and temperature extremes. Drought and salinity are particularly detrimental, as they can severely affect plant growth and productivity. The R1R2R3-MYB transcription factor AcMYB3R has been identified as a key player in enhancing drought and salinity tolerance in kiwifruit. Overexpression of AcMYB3R in Arabidopsis thaliana has shown to upregulate stress-responsive genes, thereby improving drought and salt stress tolerance (Zhang et al., 2019). Similarly, the bZIP transcription factor AchnABF1 has been found to enhance cold tolerance by regulating reactive oxygen species (ROS) metabolism and osmotic stress responses (Jin et al., 2021). High temperatures also pose a significant threat, with heat shock transcription factors (HSFs) playing a crucial role in heat stress tolerance. The Hsf gene family in kiwifruit has been extensively studied, revealing that genes like AcHsfA2a are highly expressed under high-temperature conditions, contributing to heat stress resistance (Tu et al., 2023). Additionally, melatonin has been shown to improve heat tolerance by promoting antioxidant enzymatic activity and glutathione S-transferase transcription (Liang et al., 2018; Farooqi et al., 2022). 2.2 Biotic stresses Biotic stresses, such as pests and diseases, also significantly impact kiwifruit cultivation. One of the most notorious pathogens affecting kiwifruit is Pseudomonas syringae pv. Actinidiae (PSA), which causes bacterial canker. This disease can lead to severe yield losses and even plant death. The management of PSA and other biotic stresses requires a comprehensive understanding of the plant's defense mechanisms. Research has shown that transcription factors like AcePosF21, which are involved in ascorbic acid biosynthesis, play a role in enhancing the plant's defense responses against cold stress, which can indirectly affect its resistance to pathogens (Liu et al., 2023). Moreover, the identification of stress-responsive genes and their regulatory networks is crucial for developing disease-resistant kiwifruit varieties. 2.3 Physiological and yield impacts of these stresses on kiwifruit Abiotic and biotic stresses have profound physiological impacts on kiwifruit, affecting growth, yield, and overall plant health. Under salinity stress, kiwifruit plants exhibit reduced growth parameters such as relative lateral branch length, plant fresh weight, and plant dry weight. Salinity also leads to increased sodium and chloride ion accumulation, which disrupts cellular homeostasis and reduces the potassium ion ratio, further impairing plant function (Figure 1) (Abid et al., 2020). Waterlogging stress, another abiotic factor, affects root activity and energy supply, leading to reduced photosynthetic efficiency and increased ROS damage. Grafting kiwifruit onto waterlogging-tolerant rootstocks like KR5 has been shown to mitigate these effects, enhancing the plant's physiological responses and stress tolerance (Huang et al., 2013; Bai et al., 2022). Cold stress, on the other hand, triggers the biosynthesis of ascorbic acid, which helps in scavenging ROS and reducing oxidative damage. The transcription factor AcePosF21 has been identified as a key regulator in this process, enhancing cold stress tolerance and potentially improving yield under adverse conditions. Overall, understanding the molecular and physiological responses of kiwifruit to various stresses is essential for developing resilient cultivars and ensuring sustainable production. 3 Advances in Breeding for Stress Tolerance 3.1 Conventional breeding approaches Conventional breeding approaches in kiwifruit have primarily focused on selecting and cross-breeding varieties that exhibit natural tolerance to various environmental stresses. For instance, grafting sensitive cultivars onto tolerant rootstocks has been a successful strategy. The use of KR5 (Actinidia valvata) as a rootstock has shown significant improvements in waterlogging tolerance, enhancing photosynthetic efficiency and reducing reactive oxygen species (ROS) damage in grafted plants (Bai et al., 2022). Similarly, micrografting techniques have been employed to evaluate and enhance drought tolerance in kiwifruit cultivars, demonstrating significant differences in physiological and biochemical responses under stress conditions (Bao et al., 2019).
RkJQdWJsaXNoZXIy MjQ4ODYzMg==