Improvement of Adzuki bean in China

• Chinese Academy of Agricultural Sciences, China

Adzuki bean is native to China, where approximately five million households grow about 650,000 hectares. The grain is mainly produced in four northern provinces for use in foodstuffs (a market worth about $A1 billion) and for the $A75 million export market. In Australia, 500-1000 hectares of adzuki bean (cv. Bloodwood) supply about 400 tonnes per year of high quality raw beans to Japanese processors. This food legume could be a useful source of vegetable protein.
However, the plants tend to produce much leaf and stem but little grain. The crop is also a target for virus and fungal diseases and insect pests, both during growth and while in storage. As well, adzuki bean growth is constrained by inadequate nitrogen fixation and by sensitivity to temperature and daylength. In all, Chinese farmers consider the crop more risky to grow than cereals.

The project aimed to stimulate plant breeders to work on adzuki bean, by characterising the germplasm presently available.

The project staff formed a collection of 250 adzuki varieties that represented the core of the nearly 4000 varieties known in China. The collection was assembled in China by sampling seeds of about 300 varieties. Seeds of these 250 varieties were grown out, some in insect-proof enclosures in southern China, before sampling. The guaranteed disease-free seed was checked and multiplied in Australian quarantine before being released for use.
Secondly, agronomic characters and disease susceptibility of the plants were evaluated in a field assessment program at several sites in China over three years and in Australia over two years. In China and Australia the plants were assessed and their details entered into an evaluation database tailored to the needs of plant breeders. The aim of the database was to provide for the first time a comprehensive description of the legume genetic resources, as an aid to further research.
Promising lines were assessed more thoroughly in China, either for direct commercial use or as parents. The database was extended to include photoperiod and temperature responses obtained in further trials in Australia, and data from non-core landraces measured in China.

The adzuki germplasm was shown to fall into separate groups for northern and for southern China, with additional groups overlapping in central China. A general centre of diversity was located from the Yellow River to the Yangtze River valleys inland in middle China, including Shanxi, Henan and Hubei provinces. Each group had characteristic genotype x environment interactions, with relative growth, phenology and yield rankings altered at each assessment location.
At Harbin (latitude 45 44'N) in Heilongjiang less than 20 per cent of accessions produced seed, mainly representing the northernmost province of Heilongjiang; these were the earliest lines at all locations and apparently photoperiod-insensitive. Vegetative growth was the most vigorous at this site, which had the latest time from sowing to flowering.
At Liaoyang (42 35'N) in Liaoning all but 28 per cent of accessions from southern and middle China produced seed, and standardised growth, phenologic and reproductive data were recorded for most entries. This site also recorded the greatest mean yield and the greatest maximum yield in China, and was the second latest site in time from sowing to flowering. North Chinese accessions yielded best at Liaoyang,
Growth of some entries was severely checked by unidentified virus(es) at all sites except Henan, with site specificity for infection pattern particularly at Shijiazhuang. Only a few accessions were virus free at all locations.
At Shijiazhuang (38 2'N) in Hebei all accessions produced seed. This was also the most uniform test site as per the variance of repeated check plots in an unreplicated nursery. This was the second earliest site and second ranking for mean yield. Mean seed weight was greatest at this site though Liaoyang was nearly equivalent and the maximum value for seed weight was expressed at Harbin. The greatest yields at Shijiazhuang were shown by middle-lower northern origin of accessions.
Zhengzhou (34 31'N) in Henan was free from virus, however 20 per cent of the trial was water logged so results were complete only for the remainder. Here accessions sourced from middle China were the greatest yielders. Vegetative growth was least at this site, though it recorded the highest mean and maximum pods/plant. Seed weight was generally less and yields were medium to low.
At Ya'an (29 50'N) in Sichuan, there was a high level of virus infection, as well as insect damage to seed set. This site had the earliest mean time to flowering, was the second most vigorous in vegetative growth, but medium amongst sites for expression of reproductive traits. The best yielding group was from south-middle China, with high pod number compensating for low seed weight.
There was an association of latitude of origin with yield expression at Warwick Australia (28o10' S), with a mid-summer sowing in contrast to early summer sowing in China. There were negative regressions of yield, seed number, phenologic and vegetative growth traits with latitude of origin, but countervailing positive regressions for seed size and susceptibility to powdery mildew. This was the only location free of virus and insect damage.
The best yielding group at Warwick was from south China, but this group was not the best yielding over Chinese locations. North Chinese groups were the poorest yielding in Australia, concurring with the expression of current Australian checks from Japan at similar latitude of origin.
No resistance to bruchids was found, and most accessions showed full susceptibility to Cercospora - though a few were mildly susceptible. There was a range of seed colours besides a predominant solid red, and these were distributed within all identified groups, but with a higher frequency of dual colour red/white types in northern China.
The influence of temperature was evident. At a constant latitude, and thus similar rate of change in photoperiod, time to flowering was delayed by around 15 days at Armidale compared to Grafton across the range of lines in the core collection. Flowering occurred over an 8 week period at both sites. This delay in flowering can be attributed to a slower accumulation of temperature at Armidale where, due to the higher altitude, mean temperature was much lower than at Grafton. Later maturing lines did not reach maturity at Armidale before the onset of frost, but in comparing those lines that did mature there was a delay on average at Armidale of 25-35 days compared to Grafton.
Once the photoperiod requirement has been met for each line, phenology appears to be then controlled by the accumulation of degree-days (temperature). Phenologic response to temperature demonstrated a narrower range of flowering of 8 weeks at Grafton compared with 10 weeks at Armidale.
All core germplasm lines flowered within 60 days in conditions below 13 hours photoperiod at 25/18C, but were progressively inhibited with increases up to 18-hour days for lines from southern to northern China. Only northern Chinese material was photoperiod-insensitive.