Research on shoot growth and spatial distribution of three dwarf-growth type loquat genotypes

Abstract: 【Objective】The shoot growth and spatial distribution of three growth types of loquat (dwarf-compact-type, dwarf-open-type, and dwarf-dispersed-layer-type) were investigated in order to providereference for breeding and pruning of dwarf loquat cultivars.【Methods】The mature trees of the threedwarf-growth loquat genotypes including'Minai No.1' (the dwarf-compact-type germplasm) , 'Dapod-ing No.3' (dwarf-open-type germplasm) and'Duo No.43' (dwarf-dispersed-layer-type germplasm) un-der the natural growth condition, were selected for the experiment in the National Field Gene Bank forLoquat (Fuzhou, Fujian Province) . The experimental trees were all 10-year-old with the same stock of'Jiefangzhong'. With the main trunk as the center, tree crown was divided into cubes of 0.5 m×0.5 m×0.5 m with aluminum-plastic tube. The total number of shoots and flower clusters in different parts ofcanopy were counted, and the shoot tasselling ratio was calculated. The shoot length, shoot thickness, number of leaves and angle of shoots in different parts of canopy were measured using a vernier caliper, a ruler and a protractor respectively.【Results】The results showed that, there was obvious dissimilarityon the shoot growth and its spatial distribution among the three different dwarf-growth types.'MinaiNo.1', the dwarf-compact type was ten-year-old, and its mean height was only 181.0 cm; the total num-ber of shoots within a tree was 380, and 80% of the shoots were distributed in the layers of F2 and F3 (the height of canopy was 50.1-150.0 cm) . Shoot density was greater closer to the main trunk with anaverage shoot density of 64.0 shoot · m-3. Besides, those trees, whose sum of shoots was great, the densi-ty of shoots was high and the angle was small, were more likely to have thin shoots and short inter-nodes. Further, the ratios of tasseling shoots ranged from 59.9% to 91.0% in different regions of the can-opy, and trees with a high canopy tended to have a high ratio of tasselling shoot ratio.'DapodingNo.3', the dwarf-open type, was up to 215.6 cm high, and its total number of shoots was 164, and98.8% of the shoots were distributed on the layers of F2, F3 and F4 (the height of canopy was 50.1-200.0 cm) . Shoot density near the main trunk was low, and thus shoot density on the surface of canopyand in the medium region was higher. The highest shoot density was 18.0 shoot · m-3. The ten-year-oldtrees tended to have medium height, obvious trunk, thicker shoots and even distribution of shoots. In dif-ferent regions of the canopy, the ratio of tasseling shoots ranged from 94.0% to 100.0%, and there wasno significant difference.'Dapoding No.3'had a lower density of shoots but a higher ratio of tasselingshoots than'Minai No.1'.'Duo No.43', the dwarf-dispersed-layer type, was 280.7 cm high, and itssum of shoots per tree was 184, and 97.7% of the shoots were distributed evenly on the layers of F3, F4 and F5 (the height of canopy ranged from 100.1 to 250.0 cm) . Shoot density close to the main trunk waslow so that the shoot density in the center of the canopy was high. The highest density of shoots was27.0 shoot · m^-3 occupying the 42.2% of all the shoots. Besides, this type had an unconspicuous maintrunk, low number of shoots, low shoot density, long shoots and large shoot angle with a tassellingshoot ratio ranging from 69.9% to 100.0% in different regions of the canopy. And higher canopy tendedto have a lower tasselling shoot ratio. For the above three genotypes, we found that shoot length, shootthickness and leaf number per shoot tended to be higher while shoot angle decreased as canopy becamehigher.【Conclusion】In this study, there were significant differences among the three dwarf loquattypes. For the dwarf-compact type, its canopy is short and small, but shoot number was twice largerthan that of the other two types. Due to the fairly short shoots and its high density, shoots and leavesshade each other, resulting in the low ratio of tasseling shoots, and therefore this type is not suitable forhigh-yield and high-quality production. For the dwarf-dispersed-layer type, it has the characteristics ofhigher height and lower density of shoots, which is not conducive to improving the yield per tree. Itsshoot distribution is not good for thinning flowers and fruits and other managements. The dwarf-opentype has appropriate height, shoot number and growth vigor, and even distribution of shoots, and has ahigh ratio tasselling shoot. Therefore, the dwarf-open type is suitable for production.