![]() In this study, morphological, physiological, anatomical and transcriptomic analyses were performed on seedlings with interstock grafting (HAM, ‘Hongju’/‘Aiyuan 38’/‘Mingrijian’, and HDM, ‘Hongju’/‘Daya’/‘Mingrijian’,) and seedlings without interstock grafting (HM, ‘Hongju’/‘Mingrijian’) to explore the key mechanisms underlying the interstock-mediated regulation of citrus growth and development. However, little information is available regarding the direct effects of interstocks on scion physiology and the mechanisms of rootstock–interstock–scion interaction. In recent years, rootstock research in the citrus context has become an important topic. Rad tangerine, H), which is commonly used as a rootstock, promotes grafting affinity or grafting compatibility, and has been widely used in the production of medium-ripe citrus varieties in most regions of China. Moreover, ‘Hongju’ ( Citrus reticulata Blanco cv. For instance, ‘Mingrijian’ (M), also known as ‘Asumi’ in Japan, originated from Japan and was introduced to China in 2011, which is a mandarin hybrid obtained by crossing ‘Harumi’ ( Citrus reticulata × ( Citrus reticulata × Citrus sinensis)) and ‘Sweet spring tangelo’ ( Citrus reticulata cv. ![]() With the development of the citrus breeding industry, an increasing number of high-quality mandarin-orange hybrid varieties have been produced. ‘Ponkan’, D), a high-quality tangor, has been widely cultivated in the Sichuan Province over the past decade. ‘Aiyuan 38’ ( Citrus reticulata, A) and ‘Daya’ ( Citrus sinensis (L.) Osbeck × Citrus reticulata Blanco cv. In recent decades, the scale of citrus cultivation has expanded rapidly, particularly of the tangor type ( Citrus reticulata × Citrus sinensis, mandarin-orange hybrid), which combines the benefits of orange and mandarin, and has become increasingly popular among consumers. Ĭitrus is one of the most important fruit crops worldwide, and it is widely cultivated in the tropical, subtropical and Mediterranean regions. Interstocks regulate the growth and fruiting of scions, and overcome the incompatibility between the rootstock and scion by altering endogenous hormones, mineral elements, secondary metabolites, enzyme activity and related gene expression patterns. For instance, ‘Hongmian miyou’ was incompatible with trifoliate rootstocks, such as Poncirus trifoliate thus, an interestock of ‘Guanxi miyou’ (compatible with Poncirus trifoliata) was commonly used between the scion (‘Hongmian miyou’) and rootstock ( Poncirus trifoliata). Initially, interstocks were studied as tools to overcome the interspecific incompatibility between rootstocks and scions. Rational use of a combination of citrus rootstocks and interstocks can enhance disease resistance, regulate production period and tree dwarfing, and improve citrus fruit quality. Interstock has been applied in persimmons, lemons, peaches, apples, and other fruit trees to regulate tree size, improve fruit yield and quality, and delay tree aging. The interstock is a segment of a tree trunk grafted between the rootstock and scion. During production, part of the scion of the original adult tree is often used as an interstock, and new varieties are replaced at higher branches to form a new scion for fruit production. Interstock is an inevitable common agronomic measure during top grafting. Top grafting is the most effective way to renew citrus varieties and rapidly adapt them for market adjustments. Taken together, these findings provide novel insights into the role of interstocks in regulating and contributing to the growth and development of grafted seedlings, and will further define and deploy candidate genes to explore the mechanisms of rootstock-interstock-scion interactions. In addition, multiple key genes may be involved in plant hormone signaling, starch and sucrose metabolism, and transcriptional regulation. Transcriptomics showed that genes related to photosynthesis and photosynthetic antenna proteins were upregulated in interstock-treated seedlings, with significant upregulation of photosystem PSI- and PSII-related genes. Using ‘Aiyuan 38’ as the interstock, photosynthetic efficiency and starch content of citrus seedlings improved. Morphological and physiological analyses showed that interstocks (‘Aiyuan 38’ and ‘Daya’) significantly improved the growth of seedlings, effectively enhanced the foliar accumulation of chlorophyll and carotenoids, and increased the thickness of leaf tissues. In this study, the effects and regulatory mechanisms of tangor grafting, with and without interstocks, on the growth and development of scions were analyzed by combining morphology, physiology, anatomy and transcriptomics. Interstock is an important agronomic technique for regulating plant growth and fruit quality, and overcoming the incompatibility between rootstocks and scions however, the underlying mechanisms remain largely unknown.
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