Effects Of Lateral Branch Removal Length On Growth And Yield In Tomato Plants

Tomato(Solanum lycopersicum L.)is a widely cultivated vegetable crop in the world.Its lateral branch growth affects the above-ground morphogenesis of the plant,and good plant type is the key to the efficient utilization of light energy and the formation of yield.Tomato has strong lateral branching ability,which can form lateral branches at each leaf axil,thus competing for nutrients required for plant growth and flowering and fruiting.Reasonable pruning and lateral pruning of tomato is the key to improve population yield by using vertical space.For single-stem pruning tomato cultivated in solar greenhouse,there is still a lack of reports on the reasonable evaluation and influence mechanism of lateral pruning length on tomato plant growth and yield formation.In this study,infinite growth of bright red tomato variety’Qidali’was used as experimental material.Using single stem pruning method,5 ears per plant,4 tomato fruits per ear,water and fertilizer management using conventional production technology.According to lateral branch length,lateral branch pruning criteria were divided into seven grades,namely,the following seven treatments:T1(0-1 cm),T2(2-3 cm),T3(4-5 cm),T4(6-7 cm),T5(8-10cm),T6(10-15 cm),and T7(15-20 cm)Plant height,stem diameter,stem and leaf dry weight,root dry weight and root-shoot ratio were measured.Reproductive growth indexes such as average fruit weight per panicle and yield per plant;The labor input indexes such as the number of branching and the number of lateral branches removed in the whole growing period;The content of auxin and cytokinin in roots,ovary and basal leaves as well as the expression of signal response genes were obtained as follows:1.At the early stage of tomato growth(30 days),there were no significant differences in plant height and stem diameter among all treatments;At the middle and late growth stage(60-120 days),plant height and stem diameter both increased firstly and then decreased with the increase of lateral branch removal length,and their peak values appeared in T4 and T3treatment,respectively.In terms of root,stem and leaf dry weight of tomato plants at 120 days,with the increase of lateral branch removal length,stem and leaf dry weight and root dry weight showed a trend of first increasing and then decreasing,and reached the highest value under T4 treatment.According to the calculation of root-shoot ratio,the root-shoot ratio of T6and T7 was the largest,while the difference between T1 and T5 was not significant.The average single fruit weight of the first panicle increased gradually with the increase of lateral branch removal length.The average weight of fruit per panicle from the 2nd to the 5th panicle increased at first and then decreased.The yield of each panicle was summarized and statistically,and it was found that with the increase of lateral branch removal length,the total yield also increased at first and then decreased.The number of forking and the number of lateral branch removal in the whole growing period showed a gradually decreasing trend with the increase of the length of lateral branch removal,but the decreasing rate was larger in T1-T4 treatment and less in T5-T7 treatment.According to the above results,T4(6-7 cm)is the appropriate length of tomato lateral branch removal,which is beneficial to the growth of tomato plant and the formation of yield on the basis of giving consideration to labor input.2.The contents of auxin(IAA)and cytokinin(CKs)and the expression of related genes in roots,ovaries and basal leaves treated by T1,T4 and T7 were analyzed to reveal the mechanism by which lateral pruning affects the growth and yield of tomato by regulating hormone signals between plant organs.Root IAA concentrations in T4 and T7 were 61.6%and 121.1%higher than those in T1,respectively,while the four morphologies of T4 and T7 were significantly lower than those in T1.Gene expression analysis showed that the root auxin synthesis gene FZY1 had no significant change among all treatments,but the expression of signal transduction genes(IAA16,ARF5 and ARF7)were significantly affected.At T4 and T7,the synthetic gene IPT2 and the oxidation gene CKX2 were up-regulated,while the activation gene LOG2 and signal transduction genes TRR3/4 and TRR7/15 were down-regulated.Expression analysis of auxin influx(AUX1)and outflow(PIN1)genes showed that the expressions of AUX1 and PIN1 increased with the increase of lateral branch pruning length before pruning.After lateral pruning,the expression levels of AUX1 and PIN1 in all treatments were significantly higher than those before lateral pruning,but the differences between different treatments were no longer significant.The contents of IAA and CKs in ovary and their signal transduction genes increased with the increase of pruning length of lateral branches at 5 days after pollination.With chlorophyll content,dark adaptation under maximum photochemical efficiency(Fv/Fm)and net photosynthetic rate(P_N)as evaluation index of leaf senescence,found that the chlorophyll content of the T4 treatment basal leaves,Fv/Fm,P_Nand content of IAA and CKs were significantly higher than that of T1 and T7 has to deal with,but FZY1 and IPT2 in the expression differences between the groups was not significant,while the PIN1 and CKX2 declined with the increase of lateral branch cutting length,and the aging control gene(CRF6、MYB2、SAG12 and ORE1)expression and aging phenotype.These results showed that when the lateral branch length of tomato reached 6-7 cm,it should be pruned,which was conducive to the transportation of IAA synthesized by lateral branch to root,activating root auxin signal,inhibiting CKs signal,and promoting root growth.The vigorous roots not only increase the uptake of water and mineral nutrients,but also produce more passive CKs,which are transported upward to fruit and leaves,promoting cell division of young fruit and inhibiting leaf senescence at the base.Secondly,the polar auxin transport flow formed by the downmigration of IAA from lateral branches also inhibits the outflow of IAA from stem and basal old leaves,which is also conducive to fruit enlargement and delaying leaf senescence.This study revealed the mechanism of lateral pruning length on the growth,development and yield formation of tomato plants from the perspective of hormone balance,and provided theoretical and technical support for the determination of lateral pruning length standard in single pruning tomato production.