וַיִּישָׁ֕ן וַֽיַּחֲלֹ֖ם שֵׁנִ֑ית וְהִנֵּ֣ה ׀ שֶׁ֣בַע שִׁבֳּלִ֗ים עֹל֛וֹת בְּקָנֶ֥ה אֶחָ֖ד בְּרִיא֥וֹת וְטֹבֽוֹת׃
И он спал и мечтал во второй раз, и вот, на одном стебле встало семь колосьев кукурузных, хороших и добрых.
Chizkuni
עולות בקנה אחד, “rising on a single stalk;” this was an allusion to plenty, abundance. The message had now become more explicit than in the first half of the dream. Normally, the seven kernels would compete with each other for the nutrients provided by a single stalk. In this dream they did not do so. They were all fully developed.
Rashbam
בקנה אחד, this was a symbol of plenty, seeing that each stalk had seven ears of grain