| This experiment selected fourteen plant height mutant near-isogonic lines and two brittle culm mutants from rice cultivars"Nipponbare"and"9311", which were obtained by irradiation with low-energy ion beam. In this paper, mutants were systemically investigated agronomic character, lodging resistance from variation of culms height and component; discuss the lodging factors except plant height and straw resource utilization .The results indicated:1 The relationship between plant height and lodging resistance: fourteen plant height mutant near-isogonic lines (plant height was from 75.3cm to 133.0cm, average for 109.7cm) were investigated the lodging resistance. The results indicated: when plant height increased, lodging resistance of basal internodes enhanced, but lodging resistance ability decreased. The most important factors which influence plant lodging were height of center of gravity, yield per plant, plant height and second internode length, they were positively correlated with lodging resistance, correlation coefficient were 0.743**,0.704**,0.681**,0.667**, respectively. Besides, there were some other factors which effect plant lodging, such as spike length, length of basal internodes, the weight of main stalk, thousand-grain weight and biological yield.2 The effect of plant height on agronomic characters: when plant height increased, height of center of gravity moved up, the length of second and third internode increased, and main stem fresh and dry weight increased. The relationship between plant height and yield characters showed: plant height were positively correlated with spike length, thousand-grain weight, yield per plant and biological yield, correlation coefficient were 0.889**,0.834**,0.726**,0.772** , respectively. In the dwarf rice varieties, it is feasible to increase yield by improving plant height, while biological yield increased with the increase of plant height. Coefficient between plant height and economical coefficient was not significant, and correlation coefficient was -0.079.3 The effect of tall plant height mutants on agronomic characters: we selected four plant height mutants (plant height was about 130.0 cm) from rice cultivar"Nipponbare". The result indicated: lodging resistance decreased with the increase plant height, content of soluble sugar and cellulose reduced. But, length of basal internodes and culms diameter increased. There was no obviously difference between the tall plant height mutants and"Nipponbare", such as culm thickness, first leaf length, root activity, relative chlorophyll content, and number of vascular bundle. In those mutants, there was significant difference in lodging resistance. In other words, not all varieties of tall stem bring plant lodging.4 Study on lodging resistance and component of brittle mutants: we selected two brittle culm mutants (plant height were115.5 cm and 74.5 cm, CK 122.9 cm) from rice cultivar"9311". The result indicated: break strength of basal internodes decreased, but in the field. There were no obviously difference between the tall brittle culm mutants and"9311", such as plant height, spike length, number of productive ear, height of center of gravity, internodes length, culms diameter, culm thickness. Most properties were no obviously difference between the low brittle culm mutant and"9311", spike length and height of center of gravity decreased with the decrease of plant height. For the two brittle mutants, seed setting and cellulose decreased, the content of soluble sugar and hemicelluloses increased and lignin remain unchanged.During the breeding for high-yield, it is necessary to improve plant height to get enough biological yields, but lodging will occur frequently, it is important to control plant height properly, increase dry matter of stem, culm thickness and improve physiology and genetic character of lower internodes to strengthen lodging ability. So the contradiction between lodging resistance and plant height could be settled at a level of higher yielding.
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