According to Jewish law, the fruit of a newly planted tree cannot be used for the first three seasons. During that time any fruit that is produced is orla and is prohibited. In the fourth year the fruit is neta revai which must be brought to Jerusalem and eaten in a state of ritual purity. Only in the fifth year will the fruit be permitted to be used normally.
Our Gemara brings the ruling of Rabbi Abbahu quoting Rabbi Yohanan according to whom this same rule will apply even if a “younger” branch bearing fruit is grafted on an “older” branch (one that is already more than five years old) – even in a case when the fruits continued to develop and grew more than 200 times their original size (under ordinary circumstances, if orla gets mixed in with more than 200 times permissible fruit, the orla will become nullified from a halakhic perspective).
Most of the commentaries limit this ruling to a case where the grafted branch already had fruits on it at the time it was attached to the “older” tree. According to the Rashba, if the “younger” branch was empty of fruits at the time it was grafted on to the “older” tree, we would view it as part of the tree and its fruits would be permitted.
Grafting trees is done in a number of ways, and it is an important part of agricultural work. When a farmer wants to improve or diversify the produce growing on his trees, one of the most common methods to use is grafting, where a branch is connected into – or onto – a mature tree of a similar kind. In our case, the Gemara uses the expression yaldah she-sibkhah bi-zekenah – when a young branch is connected with an older tree. Sibkhah implies complication or confusion, which may indicate that this case is not a normal situation of grafting – which is called harkava – but perhaps a case where the branch remained partially connected to its original tree at the time of grafting, and was not removed from it until it had become fully integrated with the older tree.