THE INFLUENCE OF INFECTION WITH NOSEMA APIS ON THE ACTIVITIES AND LONGEVITY OF THE WORKER HONEYBEE

Infection of the adult worker honeybee with Nosema apis reduces or obviates brood feeding and causes her to commence foraging earlier than a healthy bee. The length of foraging activity and the total length of life of infected bees is reduced.
In colonies infected with N. apis the rate of brood rearing is severely depressed during April, May and June, the degree of depression being proportional to the percentage infection.
Infection decreases during July, August and September, and consequently the rate of brood rearing increases, but the resulting addition in foraging population is usually too late to increase the honey crop.     

STUDIES ON THE EFFECT OF ASSOCIATED SOIL MICROFLORA ON FUSARIUM UDUM BUTL., THE FUNGUS CAUSING WILT OF PIGEON-PEA (CAJANUS CAJAN (L.) MILLSP.), WITH SPECIAL REFERENCE TO ITS PATHOGENICITY

The interaction of certain soil saprophytes and Fusarium udum , the wilt organism of pigeon-pea, with special reference to their effect on pathogenicity, has been studied. The filtrates of Aspergillus niger, Rhizopus nigricans and mixed filtrates of all the saprophytes inhibited the growth of Fusarium udum on solid medium. This inhibition of F. udum has been shown to be due to unfavourable reaction of the medium rather than to food exhaustion or the presence of toxic substances. The culture filtrates after passage through soil beds failed to affect adversely the growth of F. udum because of the change in pH. Inoculation experiments have indicated that only Rhizopus nigricans is effective in reducing the incidence of wilt because of its faster rate of growth. The mixed inocula of the organisms and mixed filtrates of all the saprophytes have also been observed to be effective in reducing wilt incidence. Aspergillus terreus appears to enhance the virulence of Fusarium udum.     

Behaviour of the fungus Rhizoctonia solani Kiihn in the soil

Rhizoctonia solani was found able to grow as a saprophyte through natural unsterilized soil. Its rate of growth under different soil conditions in glass tumblers was studied by the Rossi-Cholodny soil-plate method. Growth was most rapid at the lowest soil-moisture content tested, viz. 30 % saturation, and was accelerated by forced aeration of the soil. The maximum distance to which mycelial growth could be supported on the food reserves of the agar inoculum alone was some 5 cm., as shown by extent of growth through tubes of moist sand, but in 23 days the fungus grew 21–24 cm through tubes of soil. Removal of the agar disk 2 days after inoculation of the tubes reduced growth through sand by more than half, but through soil by only a small proportion. In soil, Rhizoctonia was able to cause 100% damping-off of radish seedlings planted at a radial distance of 4 cm. from the agar inoculum, and some 40 % damping-off at a distance of 9 cm. The depressing effect of additions of 1 % ground-wheat straw or dried grass to the soil upon growth of the fungus was attributed to (1) the negligible cellulose-decomposing ability of Rhizoctonia, (2) nitrogen starvation of the mycelium, through rapid utilization of the available soil nitrogen by the cellulose-decomposing micro-organisms multiplying upon the fresh organic material, (3) fungistatic action on Rhizoctonia of the respiratory carbon dioxide produced by the cellulose-decomposers.     

Value of phloem necrosis in the diagnosis of potato leaf-roll

In plants infected with leaf-roll virus a type of phloem obliteration and necrosis occurs which is distinct from any abnormality produced by other pathogens or arising from physiological causes. The necrosis occurs in the primary phloem only of the bicollateral bundles. The affected tissue reacts with phloro-glucinol in HCI. It was present in all of 179 plants of 33 varieties showing secondary leaf-roll which were examined and was not found in any of 83 healthy plants of 20 varieties. The amount of necrosis varies in different plants. If the disease is severe, necrosis may extend to almost all parts of the plant except the stolon, tubers and roots. If the infection is mild it may be confined to a very few strands in two or three nodes near the base of the main stem. Phloem necrosis can always be found before leaf rolling is apparent.
In primary leaf-roll, slight necrosis can be found in the stem near the bases of the lowest rolled leaves and sometimes in the petioles.
A technique is suggested for the use of this symptom in diagnosis.     

ON THE STEM AND BULB EELWORM (ANGUILLULINA DIPSACI KUHN) WITH SPECIAL REFERENCE TO ITS OCCURRENCE ON WEEDS OF ARABLE LAND

The importance of wild hosts of Anguillulina dipsaci Kühn as carriers of infection needs no emphasis. The occurrence of the eelworm in the weeds, cleavers ( Galium aparine ) and duckweed ( Stellaria media ) taken in crops of oats and field beans which were themselves suffering from stem eelworm disease, was recorded by Johnson (1936) and Johnson & Thompson (1937); Walton (1937) confirmed the occurrence of infested cleavers plants in eelworm-infested oats. Walton also stated that experiments indicated that seed oats failed to carry eelworm infection, and from circumstantial evidence similar to that recorded by Johnson (1936) stated that "infestations of oat crops which occur, even after the absence of the crop for more than six years, are in all probability attributable to weeds rather than to infested seed". The present writer failed to obtain living eelworms from oat seed from infested crops in Yorkshire. This paper summarizes the results of field observations and experiments accumulated mainly during the past three years.