The modifiability of characters important in potato breeding

About 2,600 potato clones of 29 combinations were repeatedly analyzed for some years at a stretch in order to determine the degree of modifiability of both a large number of separate characters and the general impression of underground plant parts on lifting in an early stage, in the mature condition and on assessing tuber samples.The ultimate aim of these investigations was to find out how far strictness is justified when selection is applied in breeding new potato varieties. Therefore correlations between the clonal generations were calculated from the data obtained for the various characters and the general impression. Only those characters for which these correlations are positive and high, i.e. slightly modifiable characters, can be strictly selected. Flesh colour appeared to be slightly modifiable. This also applies to tuber shape and maturity though these characters are somewhat more modifiable. Considerably to even strongly modifiable are eye depth, stolon length, under water weight and sprout length. Foliage type, stolon number, date of emergence and degree of common scab affection are extremely modifiable. The same is true for the general impression in the three stages mentioned above.As the general impression, in which the various separate characters and such characters as tuber number, size and yield are included, is initially decisive as to retention, it cannot but be concluded on the ground of the results obtained by others and the author that on a strict selection the major part of the most valuable individuals will be lost. This can be avoided if the negative selection takes the place of the positive in the first stages, i.e. instead of retaining only the apparently good ones the very poorest clones should be discarded in every selection stage. Not until the number of tubers suffice to lay out statistically justified tests can a change be made from the negative to the positive selection.     

A NEW TECHNIQUE FOR THE ACCURATE AERIAL APPLICATION OF HERBICIDES TO DRAINAGE CHANNELS WITH NEGLIGIBLE SPRAY DRIFT

Summary. Difficulties of access met with in Britain when applying dalapon to emergent water weeds in drainage channels led to work starting in 1964 on the development of a method of accurate aerial application of aqueous solutions of herbicide. The narrow, sinuous nature of the targets and the proximity of susceptible crops made it necessary to minimize spray drift and maintain a constant height and a slow speed. Nozzles designed to give large droplets were tested for droplet size and distribution. Selected nozzles were then tested from a helicopter in the field and the effect of their spray characteristics on the biological performance of dalapon was assessed. No daman occurred as a result of spray drift and satisfactory control of Phragmites communis, Typha angustifolia and T. latifolia was achieved with a lower dose of dalapon in a lower volume of spray than previously considered necessary for ground applications.
Une nouvelle technique pour l'application précise d'herbicides par voie aérienne sur les canaux de drainage, avec des risques négligeables d'entrainement     

THE EFFECTS ON DAIRY COWS OF GRAZING PASTURE CONTAINING HIGH LEVELS OF NITRATE-NITROGEN

Two paddocks each received a total of 412 kg N/ha (371 lb/ac) between April and July in four equal applications. The paddocks were grazed four times for four days by two groups of 5 Friesian cows starting 14 and 21 days after each N applica tion. The nitrate-N content of the herbage DM reached a peak of 0·76 % in the third grazing 14 days after N application. There was a significant (P < 0·001) correlation (r =0·67) between water soluble carbohydrates and nitrate-N in the herbage DM. No marked changes occurred in eitber the methaemoglobin or packed cell volume of the blood samples from either group. No detrimental effects on animal health or production were recorded during the experiment.