Hi Bill,
Despite growing Amaryllis bigeneric hybrids in close promixity to Hippeastrum hybrids that carry stagonsospora infections I have not had any real infection transferring to the Amaryllis hybrids. There is the occasional red colour around mechanical torn wounds in a few Amaryllis leaves but no spread or disorder in Amaryllis beyond this.
In fact the Amaryllis hybrids in my collection are generally exceptionally robust plants most of them with leaf widths of 2 inches or wider, and some have pseudo stems up to 11 inches high. I mention the latter as it is a quality not found in either parent, but often appears in the hybrid Amarylis seed plants. Those bulbs from the Brunsvigia seed parent have no pseudo bulb neck at all.
Remarkably intergeneric hybrids from Brunsvigia josephinea seed parents flower very successfully in summer dry climates in Australia, while Brunsvigia josephinea prefers a cooler summer and moist summer conditions for free flowering. The best flowering of Amaryllis hybrids occur after heavy summer rainfall preceded by one to two months of dry weather.
I'll quote from an article written by Les Hannibal in the Journal of the Royal Horticulture Society 1955:
'A chance pollination of Amaryllis 'parkeri' by A. multiflora 'Hathor' now eliminates all doubt as to the hybrid nature of these plants. In contrast to all previous seedlings obtained from either the A. parkeri or A multiflora types when selfed, this intercrossing of the two hybrid groups relased a number of genetic barriers. The floral display first observed in the summer of 1954, ranged from great broad petalled forms not unlike our best Hippeastrums to some very unusual Brunsvigia types.
Some five clones of the latter type threw radial umbels supporting distinctly chalice shaped blossoms, which were coloured a rich orange or copper red along the tube and a deep red purple or old rose on the limb. We can readily conclude that the Brusnvigia characteristics in the Amaryllis parkeri and A. multiflora types are practically wholly recessive. This is disclosed by the above seedlings which unexpectedly brought a number of latent features into evidence. Since the parental hybrids were removed several generations from the initial crossings in Australia it is evident that neither contained a full complement of the original chromosomes derived from the species Brunsvigia parentage.Thus the current hybrids are a heterogeneous mixture....................
Generally I 've found that in the climate of Sydney (highest rainfall in summer - lowest in winter), that the closer the Amaryllis hybrid is to having features like twisted petals, longer radial umbels, deep coloured yellow throats and long pseudo necks, the more robust the growth and flowering potential and frequency of the plant. While those exhibiting more species Amaryllis belladonna features are tardier in both flowering frerquency, blossom numbers and robustness. So I suspect there is an element of climatic influence in our different experiences with these Amaryllis hybrids.
Cheers
Jim Lykos