Table 14.

Comparison of the future potential of different technologies currently being applied to transfer BNF capability to cereals, and the relative benefits and challenges associated with each approach^a.

Technology	BNF potential	Advantages	Disadvantages	Timeline for delivery	Probability of success
Mucilage supported-BNF	low to medium	The trait is genetically determined by the plant and could be combined with “enhanced” microbes	Mucilage is carbohydrate-rich and may compete with grain for photosynthate	medium-term	low to medium
Endophytic bacterial enhancement	low to medium	Diazotrophs are available now that have enhanced BNF capability, already characterized to some degree	Non-specific, low population of endophytes, poor active transfer of fixed N to plants, difficult to manage, seasonal re-inoculation needed	short- to medium-term	medium
Development of legume-like nodulation by Rhizobia	high	Nodulation, a well-known system in legumes, N supply closely synchronized to crop N demand. Seed-based technology	Complex genetic engineering, genetics of plant and bacteria must interact	long-term	low to medium
Nitrogenase expression or transfer to organelle	high	Broad application to crops, N supply would be synchronized to N demand. Seed-based technology	Complex genetic engineering, expression or targeting to chloroplasts or mitochondria	medium- to long-term	medium

^aModified from Ladha and Reddy (1995); Reddy et al. (2002); Bennett et al. (2020).