Sotah, Chapter 9, Mishnah 13. Our Mishnah continues the subject of the previous Mishnah, where we learned that once the Beis HaMikdash was destroyed, the taste of the fruit and its richness were no longer what they had been. Here the Mishnah lists the causes of this decline.
What caused this decline?
"HaTaharah natlah es hata'am v'es hareiach" - the observance of the laws of tumah and taharah. In our times we lack any sense of purity, and all of us are considered tamei meis, impure through contact with a corpse or with something connected to it. Since we are not pure, the fruits were stripped of the taste and the fragrance they once had.
"HaMa'asros natlu es shuman hadagan" - the proper separation of the tithes. The tithes are called "cheilev" in the Torah, meaning the richest part of a thing, and since we do not separate them properly, the richness and abundance of the grain were diminished as well.
"VaChachamim omrim: hazenus v'hakeshafim kilu es hakol" - these two sins, immorality and sorcery, are what consumed everything and brought famine to the world.
In summary: in this Mishnah we learned the causes of the decline that followed the destruction: the absence of purity took away the taste and the fragrance of the fruit, the failure to separate tithes took away the richness of the grain, and according to the Sages it was immorality and sorcery that consumed everything and brought famine to the world.