The Keitz Meguleh in the Mishnah

מסכת מעשר שני פרק ה משנה ב

כרם רבעי עולה לירושלים, מהלך יום לכל צד. ואיזה הוא תחומה--אילת מן הדרום, עקרבת מן הצפון, לוד מן המערב, והירדן מן המזרח. ומשרבו הפירות, התקינו שיהא נפדה סמוך לחומה. ותנאי היה הדבר--אימתיי שירצו, יחזור הדבר לכמות שהיה. רבי יוסי אומר, משחרב בית המקדש, היה תנאי זה; ותנאי--אימתיי שייבנה בית המקדש, יחזור הדבר לכמות שהיה.

Mishnah Masechet Maaser Sheni, 5:2

Kerem Revai goes up to Yerushalayim up to a days walk on all sides (that is to say that there is a rabbinical decree that Kerem Revai is not to be redeemed, but only eaten in Yerushalayim if it is within these boundaries). And what is the boundary? Eilat from the south, Akravat from the north, Lod from the west, and the Jordan from the east. And when the fruits increased in quantity, they made a ruling that it could even be redeemed right next to the walls (of Yerushalayim). And a condition was made on the matter, that whenever they will want, it will return to as it was (and all fruits from within a day's walk will be eaten in Yerushalayim). Rebbi Yose says: When the Beit haMikdash was destroyed, there was this condition. And they put a condition on it, that when the Beit haMikdash will be built, it will return to as it was.

תלמוד ירושלמי מעשר שני, דף כט עמוד ב

אמר רבי אחא זאת אומרת שבית המקדש עתיד להיבנות קודם למלכות בית דוד דכתיב (דברים לב) ודם ענב תשתה חמר ואת אמרת הכין

Talmud Yerushalmi, Maaser Sheni, 29b

Rebbi Acha said: This proves that the Beit haMikdash will be built before the arrival of the kingdom of the house of David (i.e. Moshiach ben David), as it is said: (Devarim 32) "And the blood of grapes you drank as a foaming wine", and you say thus?

That is to say: Ha'azinu speaks of the last generations. In this, we see that the fruits of the land will be of great abundance. The reason for the disagreement in the Mishnah is because the two reasons given coincided: The fruits decreased at the time of the destruction of the Beit haMikdash, and so too the rebuilding of Yerushalayim and the Beit haMikdash will coincide with an increase of the fruits of the land.