FLOWERING HABITS OF DICHANT.HIUM ANNULATUM, Stapf., DICHANTHIUM CARICOSUM, A. Camus AND BOTHRIOCHLOA IIVTERMEDIA (Br.) A. Camus BY J. G. OKE (Botany Section, College of Agriculture, Poona) Received May 15, 1950 (Communicated by Prof. L. S. S. Kumar, r.A.sc.) A KNOWLEDGEof the flowering habits of grasses is of prime importance to a grass breeder in devising suitable methods of controlled pollination. Observations on the flowering habits of D. annulatum, D. caricosum and B. intermedia are described in this note, as no such work appears to have been done previously on these species. The time interval between the various stages commencing with the appearance of the flag-leaf of the boot to complete anthesis of the panicles in the above three species was studied. This information was required for purposes of selfing and bulk emasculation which involves bagging in the former case and hot-water treatment in the latter prior to anthesis. Bagging done earlier resulted in the boot tearing through and growing out of the bags. Hot-water treatment given early in the boot stage gave no useful results. REVIEW OF LITERATURE Grasses bloom, i.e., extrude their stamens and liberate pollen most abundantly in the early morning. This is an almost universal rule (Beddows, 1931) although the period of flowering may be delayed and pro- longed by clot.dy atmospheric conditions. For several grasses there is apparently a second less intensive anthesis period in the afternoon. Fruwirth (1916) found a secondary blooming period in the afternoon that lasted for one or two hours. Sando (1936) found in the Agropyron elongatum, (Host) Beauv., the maximum anthesis between 6 and 8 A.M. but there was a second wave between 3 and 4 P.M. He observed that blooming was most active when the sun was shining and the temperature was 70 ~ F. or above. No blooming was ever observed at temperatures below 52 ~ F. He believes the delay or reduction in the anthesis caused by a cloudy sky is due more to the lowering of the temperature than to increased humidity. The views of Sando (1936) respecting the effect of humidity are confirmed by the studies of Stephens and Quinby (1934) in Sorghum. They concluded: "Relative humidity apparently did not influence the time of blooming" B4a I65 166 J.G. Oke

They found that under field conditions the rate of blooming was highest shortly after mid-night. Further, a relatively small proportion of flowers opened before 10 P.M. or after 8 A.M., but there was no hour in which flowers were never found opening. They also observed that light conditions were a most important factor governing the time of blooming and that lowering the temperature reduced the rate of blooming. Fruwirth (1916) agrees with Stephens and Quinoy (1934) regarding the effect of humidity but not as to light. He found that Rye grass and Orchard grass (Dactylis glomerata, L.) bloomed in spite of the lack of light. Rece,at investigations have emphasised the importance of the relative proportion of daylight and darkness in the reproductive processes of plant development. In Orchard grass (Daetylis glomerata, L.), Wolfe (1925) found that 76.4% of the flowers bloomed from sunrise to noon, 6"6% from noon to sunset and only 0" 3% from sunset to mid-night. Jenkin (1924) found that Tall oat grass [Arrhenatherum elatius, (L.) Mert and Koch.] and Timothy (Phleum pratense, L.) unlike the perennial rye grass (Lolium perenne, L.) and red rescue (Festuca rubra, L.) begins blooming early in the morning. Kornicke (1885) reports that in Sorghum, flowering begins in the morning between 8 A.M. and 9 A.M. and may continue till evening. Graham (1916) found majority of the flowers of Sorghum opening between 2 A.M. and 4 A.M. Ramnathan (1924) found flowering period to be between 1 A.M. and 8 A.M. in Sorghum. Kornieke and Ramnathan further found that in Sorghums the dehiscence of anthers took place after they became pendant. Graham (1916) observed that it could take place at earlier stages also, in addition. At Coimbatore, Rangaswami Ayyangar and Panduranga Rao (1931) found that the dehiscence of anthers in Sorghum was simultaneous with the opening of glumes. They further found that the commencement of anthesis was not uniform but varied from 12 mid-night to 2 A.M. generally and the period between anthesis and dehiscence was 45 minutes. MA~[ERIAL AND METHODS The beginning of the reproductive phase in grasses is the impending emergence of the "boot" which is the terminal leaf-sheath. The boot presents a bulged appearance due to its enclosing a panicle or ear-head. The leaf-blade of the boot is known as the "flag-leaf ". Prior to emergence of such boots the tops of the stalks of plants assume a characteristic swollen appearance. The boots remain in a swollen condition till the panicles emerge out of them completely. For the study of the time interval between the various stages com- mencing with the appearance of the flag-leaf of the boot to complete anthesis of panicles, five plants each of D. annulatum (Bushy type), D. caricosum and Flowering Habits o)CD. annnlatum, D. caricosum & B. intermedia 167

B. intermedia were selected. Five boots, the flag leaves of which had just made their appearance were selected from each plant for observation. In order to obtain detailed information regarding the blooming process of D. annulatum, ten panicles from each of the five plants were selected and the heads marked. Each panicle possessed from 4 to 6 spikes and, therefore, ~each spike was labelled by means of small round bits of paper obtained from the punching machine. This facilitated the recording of each individual spike. Because of extreme closeness of florets the portions of the spikes over which florets opened were measured by a centimetre scale. Heads were observed at one hour interval both during day and night. Observations at night were made with the aid of a torch. The fower was considered as having bloomed as soon as the palea and the lemma were sufficiently sepa- rated so that the stigma and anther were visible. All observations were made on the bushy type of D. annulatum. In this type pedicelled florets are .neuter. In the other type of D. annulatum pedicelled florets are male and the habit of growth is spreading. Field observations were confirmed in the laboratory as follows: Five panicles each of D. annulatum and D. caricosum with about a foot of stalk were cut and placed in water in a conical flask in the evening about five hours before the commencement of anthesis.

OBSERVATIONS Data regarding the time interval between the various stages commencing with the appearance of the flag-leaf of the boot to complete anthesis of panicles of D. annulatum, D. caricosum and B. intermedia are presented in Table I below. TABLE I. Periods (in days)for various stages of panicle development beginning with the appearance of flag-leaf

D. annulalum D. caricosum B. intermedia Stage days days

1 Appearance of flag leaf to 6 6 Panicles start coming out of the complete emergence of boot boots when boots have emerged half way out of the leaf below the flag leaf. This stage is 2 Emergence of panicle from about five days from the appear- boot ance of flag leaf. Panicles begin to dehisce bit by bit as 3 From complete emergence they emerge out of the boots of panicle to commencement thus completing the processes of anthesis of anthesis and emergence of panicles simultaneously in about 4 Completion of anthesis and four days. Blooming and de- dehiscence hiscence take place during ni~,ht and early morning as in D. annu- latttm. 168 J.G. Oke

From the data in Table I it will be seen that in D. annulatum and D. caricosum a period of two days elapses between complete emergence of panicle out of the boot and the commencement of anthesis. Selfing and bulk emasculation in these species, therefore, can conveniently be done during these two days. Whereas i.n B. intermedia selfing and bulk emascula- tion have to be done during boot stage about three days after the appear- ance of flag-leaf and not later as emergence of panicle and anthesis com- mence simultaneously. DETAILS OF BLOOMING OF THE FLORETS AND DEHISCENCE OF ANTHERS IN D. annulatum At the time of complete emergence, the colour of the panicle is pale green. It remains in that condition for one day. Next day the colour changes slowly to purple-red. During the next night, .as a rule, complete anthesis takes place. If some florets or portions of spikes remain unopened they open to a very slight extent the following day but the anthesis is com- pleted during the second night. The florets bloom by opening the glumes stowly at first and then more rapidly. The stigmatic ends start protruding and about the same time the filaments of the stamens begin to elongate. These as a rule elongate beyond the stigmatic ends. About 15 to 20 minutes later the anthers dehisce apically and slowly with the inversion of the anthers the releasing of the pollen takes place. When the anther-sacs are completely emptied they collapse and appear translucent. The time required from the opening of florets to the extrusion and drooping is about an hour. The data collected showed that anthesis and dehiscence of anthers take place during the night and about 8070 of the florets open and dehisce between 9 P.M. and 4 A.M., 4" 570 florets open between 5 and 6 A.M. and from 6 A.M. onwards till 8 P.M. only 170 florets open. The remaining ones open during the following night. In every spike blooming and dehiscence generally start from 4th to 6th floret and proceed downwards. This continues till some florets at the bottom remain unopened. Then the bottom and top ends open simultaneously. Florets on some of the panMes which start blooming late in the morning between 4 and 6 A.M. rarely flower during the following day but complete their anthesis during the following night. In some spikes irregular blooming was observed. In these, florets opened at various places on the same spikes at one and the same time. In the spreading type of D. annulatum the pedicelled florets are male and which open during the night, 24 hours after the completion of anthesis Flowering" Habits o/'D. annulatum, D. caricosum & B. intermedia 169 land pollination of sessile florets. The period of blooming and dehiscence of anthers in this type is the same as in the bushy type of D. annulatum. In D. annulatum, therefore, anthesis and dehiscence take place as a rule, during night and early morning between 9 P.M. and 4 A.M. In B. intermedia blooming and dehiscence take place during night and early morning as in D. annulatum but takes about 4 days to complete emergence of panicle and anthesis of florets which processes go on simul- taneously in that species. Blooming and dehiscence of anthers 6f D. annulatum and D. caricosum observed in tile laboratory experiment showed the same sequence of pro- cesses as those observed in the field. It was observed that D. caricosum also blooms and dehisces during night and early morning at about the same time as D. annulaturn. DISCUSSION Since a period of two days elapses between complete emergence of panicle out of the boot and the commencement of anthesis, bagging can conveniently be done and large number of panicles can be bagged without fear of boots tearing through and growing out of the bags. During these two days bulk emasculation can also conveniently be undertaken. In B. intermedia selfing and bulk emasculation have to be done during boot stage about three days after the appearance of flag leaf so as to avoid any loss of seed on account of the boots tearing through and growing out of the selfing bags. For all this work butter paper bags, the seams of which had been sealed with paraffin wax were used throughout and were fastened on to the peduncles of panicles after putting a wad of cotton to allow access of air into the bags and at the same time to protect the peduncles from injury likely to be caused by the knots of strings used for tying the selfing bags. From the observations it appears that in D. annulatum pollination between florets of the same panicle is the rule the pollen from the higher and earlier opening florets falling on and pollinating the stigmas of lower florets. Cross-pollination is likely to take place in the florets which open at the commencement of the anthesis. Observations showed that B. intermedia also behaves as a self-pollinated species. Laboratory experiment showed that D. caricosum blooms and dehisces at about the same time as D. annulatum and behaves as a self-pollinated species. Satisfactory seed setting under bags (Oke, Unpublished) also lend support to the fact that D. annulatum and B. intermedia are self-pollinated species. 170 J.G. Oke

Observations of Graham (1916) and Rangaswami Ayyangar and Panduranga Rao (1931) in Sorghum compare closely with those of D. annu- latum in that the florets of Sorghum open and dehisce during night and a part of the early morning as in the case of D. annulatum.

SUMMARY

The time interval between the various stages commencing with the appearance of flag-leaf of the boot to complete anthesis of panicle in D. annu- latum, D. caricosum and B. intermedia was studied. Detailed study of bloom- ing of florets and dehiscence of anthers of D. annulatum was also carried out. In D. annulatum and D. caricosum a period of two days elapses between complete emergence of panicles out of the boots and the commencement of anthesis thus allowing sufficient time to self and treat number of panicles at a time. In B. intermedia anthesis and dehiscence take place as the panicles emerge out of the boots and thus it is necessary to bag or treat the panicles immediately three or four days after the appearance of flag-leaf. A period of 11 days in D. annulatum and D. caricosum and 9 days in B. intermedia is required from the appearance of flag leaf to completion of anthesis. In D. annulatum anthesis and dehiscence take place as a rule, during night and early morning between 9 P.M. and 4 A.M. In B. intermedia anthesis of florets and emergence of the panicles out of the boots take place simultaneously bit by bit and takes about 4 days for completion of these two processes. Blooming and dehiscence, however, take place during night and early morning as in D. annulatum. D. annulatum, D. caricosum and B. intermedia appear to behave as self- pollinated grass species. Laboratory experiments showed that D. caricosum blooms and dehisces during night and early morning at about the same time as D. annulatum. The author is greatly indebted to Professor L. S. S. Kumar, M.SC. (Lond.), F.A.SC., Economic Botanist and Principal, College of Agriculture, Poona, for his guidance and encouragement during the course of this work.

REFERENCES

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