Abstract:

In addition to sink and source, drain is also an important factor in crop yield forming. Being the organ of drain, vascular bundle (Vb) has been studied widely in recent years. In rice and wheat, researches showed that the number and area of Vb in culm (neck-panicle, branch) were positively correlated to panicle characters; cultivation factors, such as planting density, fertilizer and chemical regulator, affected the development of Vb; the Vb structure was mainly determined by cultivar type. In maize, the related studies, which started later than those in rice and wheat, have focused on the relations between Vb structure and sink capacity of ear and kernel. There are very few reports based on maize cultivar type or genotype. In maize production, vertical-type cultivars are commonly utilized. Researches showed that high yield of vertical-type cultivar is contributed by its sufficient source and large sink, however, the function of drain was seldom mentioned. The present experiments were designed to compare Vb structure and function of maize ear in cultivars with different plant types and ear types.
We choose three types of maize hybrids as tested materials, namely Yedan 4, Yedan 13, and Shendan 7, corresponding to vertical-small-ear type, vertical-large-ear type and horizontal-large-ear type, respectively. The number and area of Vb, phloem, xylem, the number and diameter of vessel were measured using bare-handed sections. The quantity of bleeding sap from ear-stalk and its sucrose content were determined. The effects of planting density and plant growth regulators on Vb structures and function and sink capacity were initially explored.
The number of big Vb and total Vb, the average area of single big Vb, total area of big Vbs, total area of all Vbs in ear-pedicel (ear-axis) of Yedan 13 and Shendan 7 (large-ear type) were significantly superior to those of Yedan 4 (small-ear type). The relative area and density of ear Vb of Yedan 4 and Yedan 13 (vertical type) were larger than those of Shendan 7 (horizontal type). The vertical -large-ear type Yedan 13 had certain superiority on the quantity and transportation rate of bleeding sap from ear-stalk. Planting density had a significant effect on the number and area of ear Vb and the response of cultivars to planting density was different. Dealing with plant growth regulators GA₃ and 6-BA could increase the number and area of big Vb in ear-pedicel. Volume of fresh grain, endosperm cells of single grain and 1000-kernel weight were also raised.

Key words: Maize, Ear type, Ear vascular bundles, Planting density, Chemical regulation