STUDIES ON OSCINELLA FRIT, LINN.: A PRELIMINARY INVESTIGATION OF THE EXTENT OF THE RECOVERY POWER OF OATS WHEN SUBJECT TO INJURY.

SUMMARY. In the summer of 1924 an investigation of the extent of the recovery power of oats after injury approximately similar to that caused by Oscinella frit Linn. was conducted under experimental conditions. The larval attack in spring was simulated by killing the growing points of the stems [(1) main stem only and (2) main stem plus first two tillers] and growth records were obtained after a limited period of time. The varieties of spring oat, Scotch Potato and Sir Douglas Haig were used, being prolific and poor tillerers respectively. The oats were sown on April 13th, were above ground on April 26th, treated (1) May 27th and (2) June 6th, the crop being harvested during the third week in August. 1. Undamaged Haig plants produced a less number of panicles than undamaged Potato plants by 21 per cent. With Potato, loss of main stem alone and loss of the first three shoots caused a reduction of about 40 per cent. in panicle production, With Haig, recovery after subjection to the first type of damage was almost complete, and as good as that exhibited by Potato after the second type of damage. 2. With regard to height of fruiting stem, a reduction of about 20 per cent. was observed after the more severe treatment with both varieties. 3. Spikeleh production varied greatly with variety, Potato carrying twice as many spikelets per fruiting stem as Haig. Tillers produced after the loss of the main stem carried no more spikelets than the normal tillers, i.e. about 30 per cent. less than the mean of the stems of the control plants. Tillers formed after the loss of three stems exhibited a reduction of 50 per cent. in spikelet production. 4. Yield of grain was not recovered by Potato after loss of the main stem (reduction 60 per cent. by weight), whereas Haig to a great extent recovered its yield. Loss of the first three stems caused a reduction of 80 per cent. in both cases, the additional reductions not however being significant in these experiments. Owing to the production of a greater number of seed, however, Potato yielded almost as well after losing its main stem as Haig did when undamaged. The variations in yield of straw were of the same order as those observed for yield of grain. 5. Recovery power after injury would appear to be much more marked with Haig than with Potato, and cannot necessarily be forecasted from a knowledge of tillering capacity. Under field conditions, where capability of covering the ground after losses may be comparatively small, as in the case of a weak tillering variety (although poor initial tillering capacity may be compensated for by an increased population), an oat like Potato might give a better yield of produce than one like Haig, even although Haig may exhibit greater recuperative powers than Potato. This problem is of course intimately related to the general problem of yield, which itself still awaits solution.