For the past four or five years, popcorn disease has been observed on a volunteer mulberry tree at Bowling Green, Kentucky. During 1984 and 1985, the diseased tree was studied carefully. The fruits were a light pink color, suggesting an identification of the tree as M. alba Each of the three branches arising from the base of the tree measured approximately 30 cm in diameter at breast height, 10 m in height, and collectively, 8 m in crown diameter. In 1985, mature leaves (N=25) averaged 6.4 cm in width and 8.6 cm in length. Leaf lobation (N= 175) percentages varied as follows: 39.4% had no lobes, 43.4% had one lobe. 12.0% had two lobes, and 5.1% had more than two lobes per leaf. More than 30 other mulberry trees in the general study area, including three with white fruits, were observed during 1984 and 1985. None exhibited popcorn disease. The three white mulberry trees were located approximately 50, 200, and 300 m from the diseased tree. Some of the red mulberry trees were within 3 to 20 m of the diseased tree. The apparent restriction of the popcorn disease to white mulberry supports previous literature reports (Siegler and Jenkins 1923, Hepting 1971). Distribution of diseased fruits was not uniform within the tree. On the lower branches (2-3 m above the ground), approximately one-half of the fruits were diseased; however, the proportion of diseased fruit decreased with in creased branch height. Orton (1903) reported that as many as 50 percent of the fruits were infected. Whetzel and Wolf (1945) found that the proportion of diseased fruits was not influenced by branch height. Diseased fruits and drupelets were larger than normal fruits and drupe lets (Figures 1 and 2, Table 1). Fruit weight and size-both length and width were statistically greater (P<0.01) for diseased than for normal fruits. The weight differences were even greater when oven-dry (700C) weights were considered. In 1985, dry matter percentages were 58.9 and 12.5 for diseased and normal fruits, respectively. Thus, replacement of the normal fruit material with fungal growth added significantly to fruit weight and dry matter percentage.

Ciboria carunculoides, in common with many other members of the genus Ciboria, is a gynicolous species. In some instances only a few of the individual drupelets composing the syncarp may be involved and in others essentially all drupelets are stromatized. The common name, "popcorn disease," is unusually appropriate for this sclerotia disease for the reason that each mature stroma (sclerotium) bears a striking resemblance in size and shape to a grain of popcorn (FIG. 1 ) .Infection occurs at a time when mulberries come into flower. This conclusion was reached as the result of direct microscopic examination by Siegler and Jenkins ( 1923), and is supported indirectly by the fact that in nature the apothecia reach maturity and ascospores are forcibly discharged at this time. The disease is not evident, however, until three or four weeks after anthesis. It may be noted then, that some of the drupelets are larger than the remainder, and that sticky, grayish, columnar extrusions are prominently present at the tips of these affected drupelets (FIG. 3).Soon thereafter the sepals. of healthy fruits are becoming fleshy whereas diseased ones remain firm and corneous. These differences become more marked as the time approaches for normal fruits to ripen. Mature stromatized drupelets are always considerably larger than healthy ones and are always grayish-; i.e., they never assume the color of mature normal drupelets. The forcible expulsion of ascospores and their dissemination by convection currents. is an efficient means of scattering the inoculum( ascospores), as shown by the distribution of diseased fruits throughout the trees. During each of the three seasons covered by these studies all the mulberries borne on the row of trees under observation were severely attacked. These trees are approximately 30 feet tall. Fruits borne on the lowermost branches were neither more nor less abundantly parasitized than those borne on the topmost branches. The abscission of diseased fruits occurs in late June and early July; i.e., at the same time that the healthy ripe fruits are being shed from disease-free trees growing a few blocks away.