Resistance Mechanism Of Alfalfa Varieties(Lines) To Therioaphis Trifolii

In this paper, four representative alfalfa varieties(lines) were chosen as tested materials, HA-3(HR), Gannong 3(R), JinHuanghou(MR) & Hunter River(LR). The resistance mechanism of alfalfa varieties(lines) to Therioaphis trifolii was preliminarily studied under the conditions of temperature control.1. The antixenosis of alfalfa varieties(lines) to Therioaphis trifoliiUnder the conditions of constant temperature(25℃), the difference of antixenosis of HA-3, Gannong3, Jin Huanghou & Hunter River to nymph was not significant in alfalfa's three periods (3-leaf- period,6-leaf-period,branching period ); as to adult, the same as nymph in 6-leaf- period & branching period, the average population was the most on the Gangnong 3's leaves in 3-leaf-period, so its antixenosis was the worst, and its antixenosis was significantly different from other three varieties(lines) (P<0.05). The antixenosis of Hunter River and Gannong 3 to nymph and adult were worse in 3 periods, and that of Jin Huanghou and HA-3 were relatively better.As the alfalfa plants growing, the antixenosis of Gannong 3 to nymph and adult were increasingly stronger, and the range of change was great. The antixenosis of Jin Huanghou and HA-3 to nymph and adult were stable in 3 periods.2. The antibiosis of alfalfa varieties(lines) to Therioaphis trifoliiUnder the conditions of constant temperature(25℃), the survival rate of nymph was high on Hunter River's(49%) and Gangnong 3's leaves (42%) in branching period. It was only 3% on HA-3 in 3-leaf-period, and the difference of HA-3 and Hunter River/Gannong 3 was distinctively significant (P<0.01). The difference of survival rate was not significant on different alfalfa varieties(line) in alfalfa's 6-leaf-period. In branching period, the survival rate of nymph was only 17% on Jin Huanghou's leaves,and the difference of Jin Huanghou and Hunter River/Gannong 3/HA-3 was significant (P<0.05).The difference of growth time of the 2nd, 3rd, 4th and 5th instar was not significant on 4 alfalfa varieties(lines)'leaves in branching period. The growth time of the 1st instar nymph was 28.8h on Jin Huanghou, and 24h on HA-3, but was only 16.8h on Hunter River. The net reproduction rate was the highest on Hunter River( 66.77). The mean generation time was the longest on HA-3(15.31d), and the order was HA-3>G3>JH>Hu. The intrinsic rate was the highest on Hunter River(0.53); and was the lowest on HA-3( 0.45). The order of finite increase rate was G3>Hu>HA-3>JH. Therefore, the antibiosis of HA-3 to Therioaphis trifolii was better.3. The tolerance of alfalfa varieties(lines) to Therioaphis trifoliiUnder the conditions of indoor temperature, the difference of growth ratio of HA-3 and Hunter River wasn't significant among different population density treatment(5,10 and 20 )after damaged 5 days, moreover, and the difference of growth ratio of Jin Huanghou and Gannong 3 was significant between different population density treatment and CK(P < 0.05). Growth resumed 30 days later,concerning the growth ratio, HA-3 and Gannong3 didn't have significant difference among different population density treatment. Compare to CK, the growth ratio of HA-3 fed by population density 20 was less than19.82 %, however, the growth ratio of Hunter River fed by the same population density was less than 98.57 %.Growth resumed 30 days later, the difference of DW/FW ratio of HA-3 was significant between population density 20&CK(P<0.05), the same as Hunter River(P<0.05). As to Gannong3, the DW/FW ratio of plant fed by population density 20 &10 were different from CK(P<0.05). As for Jin Huanghou, there wasn't significant difference among different population density treatment. When population density were 5 and 20, the difference of branching No.wasn't significant among four alfalfa varieties(lines). when population density was 10, the branching No.of Jin Huanghou was the most. Therefore, the tolerance of HA-3 wasn't significant.