Comparative Studies On Anatomical Structure Of Roots In Two Citrus Somatic Hybrids And Several Primary Rootstocks

The rootstock was the basis on which fruit trees grow. Distinct differences inaerial part growth, bearing and so on was found between the trees using differentrootstocks. The structure character of vessel element plays an important role in theabsorbing and transporting ability, then affects the aerial part growth. By means ofparaffin method and tissue segregation process, the vessel elements and xylem ofcommon and citrus somatic hybrid rootstocks were comparatively studied, and the shapeof vessel elements was quantitative analyzed. With analysis of root transverse structure,the shape of vessel element and the quantity character analysis, it was found that:1. The transverse structure of rootstocks(1) The root xylem and phloem of ordinary rootstocks assumed the concentric circlearrangement. But the somatic hybrid rootstocks red tangerine+trifoliate, red tangerine+rough lemon root xylem and phloem actually arranged unusually.(2) Xylem/traverses area. For ordinary rootstocks, this ratio ranged from 0.19 to 0.33,with the biggest and lowest values existing for swingle citrumelo and trifoliaterespectively. In comparison with the ordinary counterparts, the ratios of these two somaticcells hybrids (0.2112 and 0.0594 for red tangerine+rough lemon and red tangerine+trifoliate respectively) are less.(3) Trachea total area/xylem area. The range of this ratio for ordinary rootstocks is0.0067～0.0109, with the order: rough lemon＞troyer cirange＞swingle citrumelo＞redtangerine＞trifoliate. Compared with the ordinary rootstocks, the ratios of the two somaticcells hybrids (0.0174 for red tangerine+trifoliate and and 0.0093 for red tangerine+rough lemon) are higher.(4) Total trachea area. For ordinary rootstocks, the total trachea area varied in therange of 7.666×10⁴～3.215×10³ mm², with the order rough lemon＞red tangerine＞swingle cirumelo＞troyer citrange＞trifoliate. The area of two somatic cells hybrids werechanging with their paraents, red tangerine+tough is bigger, meant 2.430×10³ mm²,redtangerine+trifoliate is smaller, meant 6.901×10^-4mm².(5) Vessel density. For ordinary rootstocks, the range of vessel density is252.692～408.907 no./mm², with the order: swingle citrumelo＞rough lemon＞troyercitrange＞trifoliate＞red tangerine. Vessel densities of the two kinds of somatic cellshybrids fall out of the scope of ordinary rootstocks. The biggest vessel density (530.3 no./mm²) appeared for the red tangerine+trifoliate, with the smallest value (224.8no./mm²) for the red tangerine+rough lemon.In conclusion, All parameters of transverse structure were less for trifoliate. And twosomatic cells hybrids exhibited irregular root system transverse structure. The redtangerine+trifoliate almost always exhibited the biggest value for all the parametersexcept the minimum value for xylem area/traverses area and total trachea area. Except thetrachea total area, all the other parameters were low in red tangerine+rough lemon.2. Vessel elements of seven citrus rootstocks(1) Vessel element shapeCitrus rootstock's vessel elements all belong to pitted vessel, with perforation platebeing simple and distributed always in end wall. As far as the tail character beingconcerned, they can be summed up to three types: both tails, only one tail, and no tail forthe end wall. The vessel elements can also be included as: both slopes, only one slope andno slope. All the intervascular pittings are alternate pitting, with the pit orifice being theslit shape abduction and partly synthesized.The ratios of caudated vessel elements appear relatively higher in the two kinds ofsomatic hybrid than in others. The most sidewall perforation vessel elements (5%)appeared in the trifoliate, and 1～2% for the other varieties whose paraents was trifoliate.The most beginnings and ends wall inclines appear in the swingle citrumelo and redtangerine+trifoliate.(2)Vessel element diameter and lengthAmong ordinary rootstocks, the biggest Vessel element diameter (35.8μm) wasrough lemon, with the order: troyer citrange＞red tangerine＞swingle citrumelo. Thetrifoliate owned the least diameter, 26.1μm. The longest and shortest vessel elementlengths (261.9μm and 202.2μm) were owned by the troyer citrange and rough lemonrespectively. The diameter and length of the two somatic cells hybrids have an increasetrend for both of them higher than the parental values.