The heritability of resistance to early blight in diploid potatoes (Solanum tuberosum, subsp.Phureja andStenotomum)
The heritability of resistance to early blight caused byAlternaria solani (Ell. & Martin) Son was estimated for field grown, diploid potatoes at Fletcher, North Carolina in 1981. Fourteen breeding lines, selected from a random mated hybrid population ofSolanum tuberosum, subsp.phureja andstenotomum, were used. Resistance was measured as the slope obtained by regressing the logit of the disease proportion Y, measured as % defoliation, on time. A wide range of resistance was found. Narrow-sense heritability, as determined by offspring-midparent regression, on an individual plant basis, was calculated to be 0.825.
Screening potatoes for field resistance to early blight
A satisfactory method has been developed for screening potato clones for field resistance to early ligbht. Differences in clonal resistance can be evaluated and have proven to be consistent. Resistance to foliar infection appears to be generally associated with plant maturity. Late maturing selections are generally quite resistant and early maturing selections are usually extremely susceptible. Differences in resistance among named varieties from throughout the world were extremely variable.
Some properties of three related viruses: Andean potato latent, dulcamara mottle, and Ononis yellow mosaic.
SUMMARY: Three similar and apparently previously unrecorded viruses were studied and found to be most like viruses of the turnip yellow mosaic group. Andean potato latent virus (APLV) was obtained from primitive cultivated potatoes collected in the high tropical Andes, dulcamara mottle virus (DMV) from Solanum dulcamara L. growing near Rothamsted, and Ononis yellow mosaic virus from Ononis repens L. growing in many parts of England. All three viruses are readily transmitted by sap inoculation; APLV and DMV are transmitted through the seed of infected plants; DMV is transmitted by the flea beetle Psylloides affinis Paykull. Plants infected by one of the viruses are not protected against infection by the others.
Purified preparations of these viruses have many common properties. Each virus has isometric particles 25-30 mμ in diameter, indistinguishable in appearance from one another and from the particles of turnip yellow mosaic virus. Preparations of each contain mainly two types of particles with sedimentation coefficients of about 115S and 55S, corresponding to infective nucleoprotein particles and non-infective “empty” particles respectively. Each contains nucleic acid with a molar base composition of about G 16% A 22% C 33% U 29%. The three viruses are serologically related; antisera titres are 8-128 times greater with homologous than with the heterologous viruses. No serological relationship was found between these viruses and turnip yellow mosaic, wild cucumber mosaic, cocoa yellow mosaic, squash mosaic and red clover mottle viruses.
Plants infected with APLV or DMV when sprayed with solutions of 2-thiouracil or 6-azauracil produced fewer nucleoprotein particles and more “empty” protein particles, than plants sprayed with water.