Vergara - 1976 - Physiological and morphological adaptability of ri

318 CLIMATE AND RICE
by adventitious roots to those by normal roots in the soil?
leijgara: No published results can answer these questions.
HUKE; Willi a negative response to nitrogen. what do you see as the best method for increasing
yields at the farm level‘?
lei-guru: At present there is very little that the farmer can do to increase grab yields. Improvement
of the variety is needed. but basic studies have to be made to determine what plant
characters should be combined t0 increase the yield potential of the floating rices.
PHUNG: Among the cultural practices (excluding water management). which one(s) do you
think can be improved to increase grain production?
Vergara: l would give the same answer as l did to Dr. Huke’s question.
Evan's: You said that Ilovrering must not occur until the water reaches maximum depth. but
when does flower initiation occur? lt would be disadvantageous to have inflorescence dilTerentiation
competing with rapid stem elongation. but maximum water depth is too brief for inllorescence
development and grain filling.
liergara: Particle initiation usually occurs alter the water reaches maximum depth. The
period of maximum water depth would vary, although this might be longer than 20 days as
shown in Fig. l. ll is true that in some cases inflorescence dilTcrentiation is competing with
rapid elongation. Panicle development might also occur when the water is receding. In this case.
there is no competition with rapid intemode elongation.
OILA: I have a comment on the remark by Dr. Evans. Even in shallow water. paniclc development
and intemode elongation are always competing with each other.
Does the intemode elongation that enables plants to float occur before llmivering stage‘?
Ibrgairu: In general, yes. However, it would vary with the duration of the peak period and we
have evidence to show that this period will really vary.
TRKAIIASIII: Floating varieties grown in Thailand are usually late varieties. and such late
varieties usually initiate panicle primordia in November and [lower in December. With the
advent of the rainy season. naturally, water continues to rise and at the peak of the rise (it
usually falls towards the end of October or early November) these varieties initiate flowering.
GHIIJJYAL: Our observation in India indicates that as flood water rises, the lCBVtSS continue to
remain above water. even with a rise of several centimeters within 24 hours. What is the rate of
elongation of deep yvatcr rice‘?
Ikvgaru:
maximum rate of 25 cmx'day' has been recorded, This rate should be sullicient to keep the leaves
above the water under normal conditions of water rise. There are cases, however, when the rise
in water level is so rapid that varieties should have rapid intcmode elongation if they are expected
to survive during those times.
T. ‘fostllnrt: Is there any possible relation between the resistance to submergence at an older
stage and the development of air-transporting system in rice tissue‘? llas any one ever examined
the air-transporting system of the older (70-da_v-old) seedlings‘?
Vergara: I am not aware of any studies comparing young and old seedlings in tcmis of airchannel
development.
VHEEILAPAT: I would like to raise several questions that could be related to the breeding of
floating rices.
l. Is there any reason why‘ farmers grow floating rice by broadcasting?
2. For breeding purpose, what characters should be the most important component of yield?
3. Is grain quality affected by deep water‘?
Vergara: l. Broadcasting is necessary for the plants to gain enough growth before water
comes in. The plants have to be at least 6 WCElCS old before the advent of flood. otherwise the
elongation of the inter-nodes will not he sufficient for the survival of the plants. In Vietnam,
they use double-transplanting instead of broadcasting. ln this case. the seedlings are more than
6 weeks old.
2. In breeding for higher grain yields, panicle number is the most important yield component
in floating rice. Our stlwey in Thailand showed that panicle number in the floating-rice areas is
around 200Fm1 as compared to the 300 to 400fm3 in the high-yielding semi-dwarf varieties.
Increasing the tillering ability of the variety is not the simple answer to this problem. Floating
rice varieties generally have "open" tillers so that increasing the number of tillers per unit area
may become ineffective-probably‘ due to a mutual shading elTect.