Direct evaluation of the effect of borer infestation on grain filling

At harvest in 1982, all the deepwater rice plants were sampled from a 4 m² area at Dubail (variety Chamara) and from a 5 m² area at Daudkandi (variety Sada Pankaish).

Individual records were made of stem dissection (borer infested or damaged internodes, numbering from the top downwards) and the amount of grain sterility (% grains unfilled) of the associated panicle. The results are given in Table VI.

The level of stem infestation in Chamara (90%) was much higher than in Sada Pankaish (37%). Grain sterility associated with infestation in the terminal internode, however, was similar in both varieties and was significantly higher than in panicles on uninfested stems in both cases. In Chamara, infestations below the terminal internode were not shown to have increased grain sterility. The situation in Sada Pankaish differed in that infestation in the third and fourth internodes was significantly associated with increased grain sterility but not with infestation in the second internode. Separate consideration of infested stems without whiteheads showed that, in Chamara, grain sterility was highest when the terminal internode was infested, but this was not significant, and in Sada Pankaish, the only significant increase in grain sterility was when infestation was in the fourth internode.

At Dubail in late September 1982, 205 rice stems each bearing a whitehead, were collected from either the variety Chamara or Boron Bawalia. In the laboratory, the stems were dissected to determine which internodes were infested and the number and species of borer larvae present. The results showed that borer infestation down to the sixth internode may be associated with whiteheads, but 94% of the whiteheads were associated with infestation in the terminal internode. S. incertulas was associated with 84% of the whiteheads, Sesamia inferens with 2% and C. polychrysus with 6%; mixed infestations accounted for the balance. In most of the other studies, larvae usually were present singly but in this instance the majority of infestations were by two or more larvae. the highest numbers of larvae found in multiple infestations were 23 of Scirpophaga incertulas and 47 of Sesamia inferens.

1982 cont. - anatomy of DWR stems

href="\dwr\ysb9.htm"