Sentence:  Wild wheat is small and hard, quite capable of looking after itself, but its heads contain only a few small kernels. Cultivated wheat has lost its <WSD>hardiness</WSD> and its self-reliance, but its heads are filled with large kernels which feed the nation. 
Meaning of the word marked with <WSD> tags:  The quality of being able to withstand fatigue and hardship; ("of a plant") the quality of being resistant to cold or other environmental conditions.