Effects of seed infection and hydration on the buildup of common bacterial blight and its impact on the yield of dry beans

Common bacterial blight (CBB), caused by Xanthomonas axonopodis pv. phaseoli (Xap), is a serious foliar disease of dry bean (Phaseolus vulgaris). A four-year field study examined the effects of different sources of infection and seed hydration on CBB development, yield components and yield in seven resistant or susceptible dry bean lines and cultivars. The five agronomic treatments examined included clean seed, diseased seed, hydrated diseased seed, clean seed with a Xap spray and diseased seed with a Xap spray. Disease development, the yield components and yield were strongly influenced by weather conditions. In comparison with the diseased-seed treatment, the use of clean (disease-free) seed reduced the incidence of CBB leaf infection in the susceptible dry bean cultivars, but no similar benefit was observed in the resistant lines and cultivars. During the three dry growing seasons, the seed hydration treatment increased the incidence of CBB leaf infection compared with the diseased-seed treatment for the susceptible cultivars, but not for the resistant lines and cultivars. In the wet growing season, no significant difference in the incidence of leaf infection was observed between the hydrated seed and diseased-seed treatments in any of the cultivars, possibly because the wet soil conditions promoted pathogen development within the bean plants that year. Seed hydration did not improve seed yield in the dry years, but sometimes decreased it under wet conditions. Therefore, seed hydration cannot be recommended for use in the production of dry beans.

Prevalence of Mosaic and Chlorotic Streak Diseases in the Sugarcane of Puerto Rico

One of the problems facing sugarcane growers in Puerto Rico is the presence of sugarcane diseases such as mosaic and chlorotic streak. A general survey of the cane fields was conducted to determine the abundance of these diseases in Puerto Rico. It was observed that mosaic was abundant in the east-central as well as the southeastern part of the Island. The abundance of mosaic in that portion of the Island can be attributed to an increase in the cultivation of the very susceptible variety B. 34104. Although this variety is now being replaced by others, some of those being propagated in new plantings are susceptible to the disease. B. 34104 is still a menace to effective sugarcane growth in the areas where it has not been completely eradicated. Another factor that helps distribute the disease is the transportation of diseased seed to be planted in places where the disease is not found. Comparing the present mosaic situation with that in 1918, when the industry was on the verge of a complete collapse, we find that the areas that now appear to be relatively free from the disease are the ones that were more severely affected in the past. Chlorotic streak disease is also present in Puerto Rico, being more abundant in the northern part of the Island. Its presence is most predominant in the rainy regions of the Island north of the divide from Mayagüez to Humacao. Probably the vector transmitting the disease is more effective in this area.

The Control of Anguillulina dipsaci on the seed of Teazle and Red Clover by Fumigation with Methyl Bromide

The stem eelworm Anguillulina dipsaci (Kühn) Gerv. & v. Ben., is responsible for disease in numerous plants, amongst which are teazle, Dipsacus fullonum L., the type host and red clover, Trifolium pratense L. In both cases seed harvested from infected plants will often be infected by the stem eelworm in spite of the greatest care in dressing the seed.Kühn (1857) in describing the parasite for the first time said:— The seeds of the diseased teazles differ from those of the healthy ones. They are not half so large nor so sharply angular. Whilst the pappus of the healthy seed is stalked that of the diseased seed is sessile and almost twice as large. The worms do not completely fill the diseased seed but occur within the atrophied ovule and also as small clumps of worms within the tissue of the abnormally thickened seed coat. The worms are found not only within the diseased seeds but in all other parts of the head including the pith where they cause not only abnormal growth but death and brown discolouration of the tissues.

Does “Tulip root” in Oats commonly arise from Seed-borne Infection?

It has been known for many years that the stem eelworm, Anguillulina dipsaci, can be carried in or upon the seeds of a number of different plants. Kühn (1858) originally found the parasite in the diseased seed heads and seed of the teasel or fuller's thistle. Bos (1888) discovered the worms in the flowers of the onion, Allium Cepa, and found in one case 3 per cent. of the seeds were infected. Godfrey (1924) found infestations of the parasite in the flower heads of cat's-ear, Hypochoeris radicata, and dandelion, Taraxacum officinale, and discovered in both hosts that living worms occurred within the seed coats. He also obtained diseased seedlings by sowing infected seed of both hosts. Hodson (1926) reported the occurrence of the parasite in quiescent form beneath the pales of oats harvested from fields badly affected with “tulip root” and obtained small numbers of infected seedlings by sowing such seed. The number of such cases was, however, so small that he considered their occurrence might be accidental. Robertson (1928) investigating “tulip root” in oats, found the parasite in the panicles of affected plants giving rise to abortive flowers. In a number of oat grains from distorted panicles he found small numbers of the parasite between the glumes and pales and between the pales and the kernel and was able to show that after storage for a few months the worms could be revived by soaking the grains in water. He did not pursue his studies to the extent of obtaining diseased seedlings from such infected seed. Cobb (1929) found samples of seed of red clover and lucerne, as cleaned by commercial processes, yielded the parasite in a living condition when soaked in water.