10 MASS. EXPERIMENT STATION BULLETIN 424 



The percentage losses by October in 1940 were similar to those in 1939, but 

 the average yields from the imported sets approached those grown from the 

 local sets. The poor yields of imported sets in 1939 may be partially explained 

 by the fact that an acute shortage of sets existed that year. Lots of very poor 

 quality were shipped in and planted. Resulting yields were low and the keeping 

 quality, in most instances, was poor. In 1940 when sets were plentiful and the 

 quality was good, there were no significant differences between the yields of 

 locally grown sets and of imported sets. However, the keeping quality of onions 

 from imported sets was definitely poorer in 1940 as well as in 1939. 



Factors Which May Affect Set Quality. — Unfortunately it is impossible, except 

 in extreme cases, to determine from the external appearance of onion seed sets 

 how the crop will yield or how it will keep in storage. Some lots were off color 

 and had a considerable amount of fungus growth on the basal plate; yet the 

 yields were good and shrinkage losses in storage were low. Other lots which 

 appeared bright and healthy gave just the opposite results. In one experiment a 

 number of sets from one lot were kept in a tightly closed container for two weeks 

 just previous to planting. At planting time the sets were moldy and musty, yet 

 they produced just as satisfactory a crop both as to yield and keeping quality as 

 those sets kept under more favorable storage conditions. To account for the 

 difference in performance between different lots of sets, it appears that studies 

 should be made to include the production and storage of the sets themselves. 

 The methods followed in each producing section should be compared. Soil 

 differences between sections should be studied and the importance of the soil in 

 each section as a source of inoculum should be determined. Do sets grown on 

 land relatively free from bulb rot fungi produce a better keeping crop of onions 

 than sets grown on old onion land? 



The conditions under which onion sets are grown in the Connecticut Valley 

 differ from those in other set-producing sections in the United States. Connecti- 

 cut Valley sets are grown on light sandy soils with only moderate amounts of 

 commercial fertilizers, while most imported sets are grown on soils which are 

 naturally more fertile even without the addition of fertilizers and are also more 

 moist. It may be that some of these factors play an important role in the keeping 

 quality of the mature bulbs which are ultimately produced from sets grown under 

 these different conditions. 



Disease in Seed Sets. — Since the culture of set onions, from seed to marketable 

 onions, requires two growing seasons, the chances of infection in the field and in 

 storage are much greater than with seed onions. Infection may take place when 

 the seed sets are grown, when they are stored in winter, when they are planted 

 for the production of marketable onions, and again when the marketable onions 

 are stored. 



It was found from examinations of roots and basal plates of seed sets, in samples 

 taken from 18 lots, that in some lots as many as 76 percent of the sets had spores 

 of disease-producing organisms on them. In samples from other lots, cultures 

 from the internal tissues of the basal plate revealed that 40 to 60 percent had 

 fungus mycelia present, in most cases Fusarium. However, there was no correla- 

 tion between the presence of spores on the surface or of mycelia in the tissues of 

 the seed sets and the amount of rot which developed in storage in the onions 

 grown from the sampled lots. In some cases, the onions from apparently clean 

 sets rotted badly; in others, onions from apparently heavily infested and invaded 

 sets developed little rot. Hence, the indication is that fungus spores on the 

 surface of the seed sets or mycelia in the tissues is not an important factor in the 

 rot of onions in storage. 



