RESEARCH WORK AT U. S. PECAN FIELD STATION BROWNWOOD, TEXASPecan Research
by L D. ROMBERG Crops Research Division Agricultural Research Service, U. S. Dept. of Agriculture The program committee has asked for a brief report on the various projects underway and the progress made on them at the U. S. Pecan Station at Brownwood, Texas. The scope of work of any experiment station is necessarily limited to what the personnel can do with the funds available. Experimental work is often slow in producing outstanding new results and attracts little attention, and some people probably doubt that it is worthwhile. That research does pay in the long run, or at least should, is indicated by the fact that most large corporations invest substantial portions of their incomes in research to develop new or better products or new or improved processes that reduce the cost of production. Imagine a corporation like Du Pont, General Motors or Wright Aircraft producing the same material, product or model of automobile or plane year after year just because it is expensive to make progress. It would soon stagnate and fail to meet competition. Some American corporations support as many as 2, 000 highly trained, highly paid scientists and expensive laboratories so that they can go forward. They would certainly not do so, were it not good business. At present our principal projects at Brownwood are concerned with pecan irrigation, tree spacing and breeding, selection and evaluation of new varieties. Though the U. S. D. A. does experimental work on the pecan at other locations, it does pecan breeding and studies irrigation of pecan trees mainly at Brownwood.
The irrigation experiments are not completed. A period of years is required for adequate results from this kind of experimental work. A little will be said here about this study. We record rainfall, check soil moisture in the orchard and irrigate certain experimental plots when the available soil moisture content becomes low. We measure every tree each winter to determine how much it grew the previous year and get accurate records of its nut production and of the size and the filling of the nuts. The results show that proper pecan irrigation at the right times increases tree growth and yield of nuts. Tree Spacing A report on the effects of tree spacing on tree growth and yield of nuts appears in the Proceedings of this association for 1956.
Breeding was started in a small way and has received increasing attention. We have not made any detailed report on this work for lack of time to prepare such a report; in fact, we have not had time to make many desirable records. The procedure followed in the breeding work may be of interest. Heredity in the pecan is by the same mechanism which plant breeders have taken advantage of to improve almost every cultivated plant. Basically the procedure in breeding is to bring together in new plants hereditary elements which determine desired characteristics and to eliminate elements which cause undesirable ones. This involves crossing of selected parents, rearing of the progeny, selection from the progeny and usually a repetition of the process for at least several generations. With the pecan the process is slower than with most other plants because of the long time required to produce a generation. To reduce this time and the space required to grow a seedling at the Brownwood Pecan Field Station we insert buds from seedlings in the first year of growth in branches of bearing trees. These buds are then given the needed after-care until the branches they produce bear nuts.
The steps in pecan breeding, then, are as follows:
(1) Controlled pollinations are made in the Spring.
(2) Nuts resulting from these pollinations are harvested in the Fall.
(3) These seed nuts are planted in the Winter.
(4) Buds from resulting seedlings are grafted to the branches of large trees in June, July or August.
(5) Branches are developed from these buds.
(6) Nut samples are harvested from these seedling branches.
(7) the seedlings are evaluated, most are discarded, a few may be propagated for trial as varieties, and of these a few may be named.
(8) The process is continued. As a preliminary to breeding it is necessary to grow trees or branches of varieties which have characteristics that are considered desirable and are to be incorporated in a superior variety. When pistillate flowers and pollen are available, we start breeding. In the station orchard we have the standard varieties and many others. These include eastern, western and northern varieties of pecan hicans and a few hickories. We now also have in production selected offspring of cresses made in the past and can use these as parents. Breeding starts with the bagging of blossoms to control pollination. The bags used are made from artificial sausage casings, which come in long, seamless tubes of a pliable, light, transparent material permeable to gases. Casings having a diameter of 1⅛ inch are cut into pieces 4¾ inches long. Then each piece is slipped onto a wooden peg and the end is twisted together and securely tied with twine, forming a tube open at one end and closed at tube other. Before the stigmas of the female or pistillate flowers have developed a surface to which pollen will adhere, the tubes are placed over the flower cluster to exclude wind-blown pollen. Previously some of the small, young leaves at the terminal of the blossom-bearing shoot are pinched off and a small quantity of quilt cotton is wrapped around the shoot at this point. The bag is then slipped over the blossom and is tied down against this padding. We begin bagging about April 15 in an early spring or a little after April 20, in a late spring. Because of the long period during which the pistillate flowers of different varieties become receptive bagging may extend over a period of about 15 days. If there is a good pistillate bloom on a tree and the wind is not swinging the branches too much a man can bag 400 or more flower clusters per day. Pollen of the varieties desired for making certain crosses is obtained by picking catkins when the anthers are ready for dehisence, or ordinarily after dehiscence has begun but, of course, before it has been completed. The catkins are spread on a sheet of paper in a thin layer and are usually covered with another sheet to prevent contamination by pollen carried in the air. As the catkins dry the anthers open and the pollen, a yellow powder, drops onto the paper. The catkins are then removed and the pollen is separated from detached florets and other materials by sieving through a cloth of medium weave, such as poplin. Some pollen is placed in storage for use the following season, and some of the pollen used each season is taken from cold storage. This is necessary because some pollen is not shed as soon as needed for certain pollinations. For storage pollen is bagged in sausage casing and placed in a closed container in which the relative humidity of the air is maintained at 10 to 20 percent by means of sulphuric acid. To attain this humidity concentrated sulphuric acid is diluted to strength of 62 percent by weight. The container is kept in a food locker in a commercial cold storage plant at zero to 5 degrees Fahrenheit. So stored, pollen has been found viable after 2 years and may keep considerably longer. Pollen is applied to the stigmatic surfaces of the bagged nutlets by means of an instrument called a pollinating syringe. This consists of a rubber bulb, in which the pollen is placed and to which is attached a 20-gauge hypodermic needle, through which the pollen is blown. The needle is inserted into the bag through the cotton pad on which the bag was tied, so that removal of the bag is unnecessary. To effect fertilization the pollen must be applied to the stigmas while it will adhere and apparently also while the ovule and the tissue in the stylar canal are in the proper state, or ordinarily during a period of about 10 days after the stigmas first have a moist, sticky surface to which pollen will adhere. The length of the receptive period varies with variety and with the weather during the period. If pollination is delayed too long pollen may adhere to a stigma without fertilization being accomplished. While pollination of an individual stigma at any time during such a long period may result in fertilization, an intermediate period is most favorable if all bagged flowers on the tree are pollinated at the same time, since they will vary in stage of development. After the bagged flowers on a. tree have been pollinated and those which may have been missed have developed well past the receptive stage, as indicated by unbagged flowers on the same tree, the bags are removed and each cluster is given an application of insecticide with a small hand sprayer made from an oil squirt can. This is to prevent infestation by the first generation of the nut case-bearer. The various operations of bagging, collecting pollen, pollinating and removing bags keep one man employed a month. The nuts resulting from controlled pollinations are planted according to an identifying pattern in a seed bed or in large cans so located that they can be observed and watered as needed. As soon as the young seedling's stem has become stiff it can be used for budding. As each stem is cut for buds an identifying metal tag is attached. At the time of budding this tag is wrapped around the stock and some three or four weeks later, when the strings are cut, the tag is nailed to the stock provided the bud has taken. In case the bud has not taken or fails to produce a branch, later the tag is removed and the seedling may be budded for a second time. Buds from small seedlings are propagated by transferring a long patch of bark by the method known as cut-and-sash budding. This patch is preferably taken off the bud stick by a somewhat spiral cut so that it contains two bud nodes. Little difficulty is experienced in getting bud patches to "take" if they are set at the right time, but it is well to have two buds of each seedling set, since strong winds or hail stones may break out some of the shoots from buds before they have developed strength. Usually only one bud patch is set from each seedling as there may be more than 1, 000 seedlings to propagate. The buds will "take" on any stock having an active cambium. They can be set on the current season growth of trees cut back the previous winter or into older branches of a diameter up to about 2 inches of trees never cut back if they are sufficiently active. After the bud has been set in place it is tied with cotton twine and sealed with melted paraffin. The wax holds the string in place after it has been cut at the back of the stock, so that each bud can easily be located when the tree is pruned during the following winter. The procedure of developing branches from these buds is the same as that followed in an ordinary top-working operation. Harvest of nuts from cross-bred seedling branches starts in September and continues until about November 1. With us it must be completed before the general orchard harvest begins to avoid a conflict of operations. Sample nuts are obtained by pulling branches to where the nuts can be reached by hand or by means of a hoop net on a pole, a stripper being attached to the pole immediately above the net. As the nuts are harvested, data, such as the seedling number, location of the branch, date of harvest, and any desired notes relative to leaf, nut, disease resistance, productivity or otherwise, are written on the paper bag container. The number of cross-bred seedlings from which a nut sample is harvested varies from 1,000 to over 2,000 per year. After the harvest of the crop from the experimental plots is completed, samples from the various plots are graded and the records on tree production and nut characteristics are compiled; then there is time to examine the sample nuts representing the progeny of various crosses. When the samples have been examined the seedlings which should be discarded are listed. Branches from such seedlings are then sawed out of the trees in which they are located. By that time another spring has arrived. The breeding program also includes the cutting of scion wood from the seedlings which appear promising, storage of the same, and propagation of the same to orchard trees at the proper time. Later, when these are in bearing, they are observed further as to the various characteristics desired in a commercial variety. The Station has 20 acres of young trees used for the propagation of these trial varieties and this acreage will probably be increased. Scion wood of promising selections is also distributed for trial to cooperating growers, who sign certain propagation agreements. These growers are very helpful in determining the merits of any selection and in making a decision as to whether a trial variety should be named.