轮回选择和穿梭育种对绿豆籽粒产量的响应

1996~2008年,选用五个中国绿豆品种,五个泰国绿豆品种,构建九个轮回选择群体。2009～2010年,在中国南京,比较上述群体籽粒产量和农艺性状的差异显著性。结果表明,轮回选择对提高绿豆籽粒产量具有显著效果,遗传增益最大的群体增产9.59%。对于以籽粒产量为主要选择目标的轮回选择来说,只需选择两个轮次,第三轮开始遗传增益会逐步下降。穿梭育种获得的轮回选择群体（K群体）平均产量比未穿梭群体（N群体）高7.26%,说明穿梭育种对提高绿豆籽粒产量具有显著效果。将同一轮次的K群体和N群体进行比较,在轮回选择第一轮次（C1）、第二轮次（C2）、第三轮次（C3）和第四轮次（C4）四个轮次中,前者分别比后者增益4.07%、8.76%、8.53%和7.98%,说明穿梭育种产量遗传增益的稳定性。N群体内变异系数明显大于K群体,表明在N群体中继续选择,获得优良家系的几率高于K群体。

The Prevalence of Mycoplasma Hyopneumoniae in Commercial Suckling Pigs in Thailand

The aim of this study was to determine the prevalence of M. hyopneumoniae infection in suckling pigs. Nasal swabs were collected from 300 suckling pigs originating from five farrow-to-finishing farms. One farm had a confirmed PRDC problem (farm A) and four other farms previously had a PRDC problem (farms B, C, D and E). Thirty (30) lactating sows in parity 1, 2 and 3 were selected from each farm (Ten sows per parity). Two piglets from each sow were randomly sampled for nasal swab at 3 weeks of age. The samples were analyzed by the nested PCR technique. Forty five per cent (27/60) of nasal swabs from farm A were found positive. On the other hand, a total of 2.08 per cent were found positive (5/240) from farm B, C, D and E. The tendency of piglet infection per sow by parity showed that first parity had more prevalence than the second and the third parity (60%, 55%, 20%), respectively. We have found a correction between M. hyopneumoniae early infection in suckling pigs and a confirmed PRDC problem (farm A) as oppose to farms that did not have a PRDC problem. The strategies to prevent M. hyopneumoniae early infection are to maintain good lactation, antibiotic prevention program and early M. hyopneumoniae