Plant Sanitation, 



322 



[October, 1909. 



A RIPE ROT OP MANGOES. 



By T. Petch, b.sc, b.a. 



Specimens of mangoes have recently- 

 been sent in from the Batticaloa dis- 

 trict, with the information that they 

 usually developed black spots when 

 ripening, and had lost the flavour which 

 characterised them in previous years. 

 The tree was a grafted mango, imported 

 from India, the fruits being of the rupee 

 mango type and above the average size. 

 The grower stated that the fruits were 

 gathered before they were ripe, in order 

 to avoid the ravages of squirrels, and 

 were kept closely packed for a few 

 days until they acquired a golden 

 colour. The ripening began from the 

 stalk end of the fruit, that end becom- 

 ing pale yellow and soft while the 

 remainder of the fruit was greenish. In 

 previous years the fruits had been sweet, 

 but now, when apparently ripe, they 

 were sour. 



Two specimens were sent. One of 

 them showed a few circular black spots 

 scattered over the surface, and was 

 turning pale yellow round the stalk, 

 the other was still green. The black 

 spots did not extend through the rind, 

 some of them were superficially cracked, 

 and contained a dark-brown irregular 

 mycelium in the cracks, but this had 

 not spread into the fruit. At first sight, 

 therefore, these spots appeared to have 

 no connection with the change of flavour, 

 but another explanation of them 

 presented itself afterwards. On cutting 

 open the fruit, the pulp below the pale 

 yellow rind was found to be watery 

 looking, contrasting strongly with the 

 firm orange flesh under the greenish rind. 

 This watery tissue extended all over the 

 top of the fruit, and down on both sides 

 of the stone. Microscopic examination 

 proved that this part of the fruit was 

 permeated by a coarse hyaline mycelium, 

 spreading in all directions between the 

 cells. The cells still contained a large 

 number of starch grains, a fact which 

 shows that ripening had not been com- 

 pleted, since in the course of the ripen- 

 ing process the starch grains are con- 

 verted into sugars. It is quite clear, 

 therefore, that the supposed ripening 

 is not a ripening but a rot caused by a 

 fungus, and that the acid flavour is due to 

 the incomplete conversion of the starch 

 grains in the immature fruits. The 

 fungus enters the fruit through the 

 stalk and spreads in all directions 

 through that end of the fruit, and 

 therefore that part appears to ripen 

 first. When it reaches the top of the 

 stone it travels down both sides of it 

 much more rapidly than in the fleshy 



parts; the rot of the tissue round the 

 stone in this ease made it possible to shell 

 out the latter after the manner of a 

 plum stone. This fruit was split into 

 two parts longitudinally, and the 

 halves were placed in a glass dish. By 

 the next morning it had developed an 

 abundant covering of greyish black 

 mycelium over all the watery yellow 

 parts but not over the firm orange 

 yellow tissue. This confirmed the result 

 of microscopic examination, that the 

 fungus was confined to the watery 

 tissue, while the luxuriant growth 

 showed what an enormous quantity of 

 mycelium the tissue contained. In a 

 few days it had spread all over the 

 hitherto sound parts. 



From a comparison of the mycelia, it 

 is evident that the restricted black spots 

 scattered over the sound fruit are the 

 result of ineffectual attacks of the 

 fungus on the fruit, most probably when 

 it was on the tree. In these cases the 

 fungus could not penetrate the rind, but 

 after the fruit had been gathered it 

 easily entered through the stalk. The 

 two effects are caused by the same 

 fungus, but the rot does not, or did not 

 in this case, extend inwards from the 

 superficial black spots. 



As is usual in such cases, the extremely 

 abundant mycelium did not develop 

 any fructification. This was obtained 

 from the second specimen, which was 

 placed, uncut, under a bell glass. In a 

 few days it turned pale yellow round 

 the stalk, as in the first example, and 

 then developed large, dull black, or 

 blackish brown patches at that end of 

 the fruit. These spots are caused by the 

 fungus attacking the rind from the 

 interior ; those previously referred to 

 were the results of its attack from the 

 exterior. Subsequently, the epidermis 

 on these patches ruptured and disclosed 

 dull brown masses of spores, from one- 

 hundredth to one-fiftieth of an inch in 

 diameter, surrounded by the upturned 

 epidermis ; and as the number of these 

 masses increased, the whole of the black 

 spots became covered with confluent 

 spore masses. These masses are pinkish 

 when dry. The individual spores are 

 hyaline and cylindric, and measure 12 * 

 to 19 microns in length and 4 to 5 microns 

 in breadth. The rotten fruits were kept 

 for several weeks, but no other fructi- 

 fication was discovered, although that 

 already described is only one stage in 

 the life history of the fungus. 



The fungus is a Gloeosporium, evi- 

 dently Gloeosporium mangae, Noack, 

 which was first found on mango fruits 

 in Brazil. Two other species of Gloeos- 

 porium have been found on mango 



