T. Visser

Acidity and sweetness in apple and pear

SummarySweetness and acidity in apple and pear inherit independently and can be organoleptically evaluated separately, but less accurately in pear than in apple. For breeding purposes an analysis of fruits for acidity and sweetness with pH indicator paper and a hand refractometer is to be prefered to the organoleptic method.In apple, the acidity-decreasing with time-of the unripe fruit was already strongly indicative of that of the eating-ripe fruit; sugar-increasing with time-not before the fruit was picking ripe. Sugar content in apple and pear, and the pH in pear, appeared to be normally distributed; the pH in apple showed a segregation into an acid and a low-acid group, which occurred in both the unripe and ripe stage. The segregation ratio between these groups was found to be highly variable. On the whole, the mean acidity and sugar content of apple and pear progenies is significantly determined by that of the parents. Most of the observations made did not support the theory that low acidity in apple is determined by one recessive gene. The relationship between the pH of leaf juice and fruit juice in apple may offer a possibility for pre-selection.SamenvattingZoet en zuur in appel en peer erven onafhankelijk van elkaar over en kunnen organoleptisch afzonderlijk worden bepaald; bij peer echter minder nauwkeurig dan bij appel.Voor veredelingsdoeleinden is de analyse van de vruchten op zuur en zoet met behulp van pH-indicatorpapier en een handrefractometer te verkiezen boven de organoleptische methode.Bij appel is de zuurheid-afnemend met de rijpheid-van de onrijpe vrucht in hoge mate positief gecorreleerd met die van de eetrijpe vrucht; suiker-toenemend met de rijpheid-pas als de vrucht plukrijp is.Suikergehalte in appel en peer, en pH in peer, blijken normaal verdeeld te zijn; de pH bij appel vertoont een splitsing in een zure en een laag-zure groep, die zowel in het onrijpe als het rijpe stadium optreedt.Het gemiddelde zuur-en suikergehalte van appel-en peerpopulaties wordt significant bepaald door dat van de ouders. Onze waarnemingen stemmen in het algemeen niet overeen met de theorie die zegt dat laag-zuur bij appel bepaald wordt door één recessief gen.De relatie tussen de pH van bladsap en vruchtsap bij appel kan een mogelijkheid voor de voor-selectie bieden.

Hybrid tea-rose pollen. I. Germination and storage

SummaryGermination and storage trials were carried out with pollen of several rose varieties. The pollen grains germinated well in a 15% sucrose solution with 40 ppm boric acid. Staining the pollen with a 0.1% tetrazolium solution and standardizing the degree of colour at which the pollen grains are counted as viable, provided a good viability estimate, simpler to carry out than in vitro germination. Germination capacity and staining ability of the pollen were greatly impeded-about halved-by dehydration during storage in desiccators at low humidity. This effect could be corrected by humidifying the pollen beforehand for about one hour, though this pre-treatment increased the percentage of germinated pollen grains more than the percentage stained. There was no difference between the two percentages in fresh or in deep-frozen pollen.Pollen stored at 1°C and high relative humidity soon lost its germination capacity: between 0 and 20% humidity a considerable proportion of the pollen remained viable for 9 months and longer. Storage for the same period in vacuum-sealed glass tubes at −24°C maintained viability as well or better and would probably prolong it further. Some of the cold-stored pollen induced a reasonable seed set after one year, a low seed set was obtained even after two years of storage at 1°C and low humidity.

Precocity and productivity of propagated apple and pear seedlings as dependent on the juvenile period.

SummaryAdult apple and pear seedlings varying in juvenile period were propagated on rootstocks. They were subsequently found to be more precocious and more productive when the juvenile period had been shorter. In view of the significant relation between vigour measured by stem diameter) and precocity of both seedlings and propagated trees, it is possible to pre-select for the potentially more precocious seedlings on the basis of vigour.SamenvattingDe vruchtbaarheid van vegetatief vermeerderde appel- en peerzaailingen in verband met hun jeugdperiode Reeds vruchtdragende appel- en perezaailingen, waarvan de voormalige jeugdperiode sterk varieerde, werden op onderstam geoculeerd. Het bleek dat de bomen gemiddeld vroeger vruchtbaar en productiever waren naarmate de voormalige jeugdperiode korter was geweest.De al eerder geconstateerde relatie tussen groeikracht en jeugdperiode (kortere jeugdperiode naarmate de bommen dikker zijn), bleek ook na vermeerdering te bestaan, d.w.z. de dikkere bomen bloeiden eerder dan de dunnere. Daar deze samenhang erfelijk bepaald is, biedt dit de mogelijkheid om de potentieel vroeg-vruchtbare zaailingen reeds in het kwekerijstadium op basis van groeikracht te selecteren.

A comparison of apple and pear seedlings with reference to the juvenile period I. Seedling growth and yield

SummarySeveral thousand apple and pear seedlings of many progenies were studied in connection with their juvenile period (J.P.). The initially significant inverse relation between the vigour (stem diameter) and the J.P. of the seedlings became insignificant as the trees grew older, due to a retardation of growth occurring when the seedlings become generative. This relation can be used effectively in pre-selecting for vigour in the nursery. Cumulative yields were higher when the J.P. was shorter, but there was no evident link between the J.P. and annual yield in full bearing, that is to say, precocity and preductivity are not directly connected. Better growing conditions and pre-selection have shortened the mean progeny J.P. of either crop by three years since the 1950s. Generally, the pear seedlings appear to grow faster, to become generative slower and to yield lower than comparable apple seedlings. The mean J.P. of apple and pear progenies averaged 4.2 and 6.0 years respectively. The difference between apple and pear may be attributable to a greater selection pressure on both precocity and productivity with apple than with pear.This possibly also led to a smaller tree in the productive phase on the assumption that tree size at first flowering-small at a short, large at a long J.P.-expresses reproductive efficiency and as such is reflected in the size of the adult tree.

Resistance to scab (Venturia inaequalis) and mildew (Podosphaera leucotricha) and fruiting properties of the offspring of the apple cultivar Antonovka

SummaryProgenies obtained from crosses between selections from open-pollinated ‘Antonovka’ and other apple cultivars and from subsequent backcrosses, were observed for resistance to scab (Venturia inaequalis) and to mildew (Podosphaera leucotricha) and fruiting characters. Scab resistance in the field greatly varied with the weather conditions. In the greenhouse or under favourable conditions for scab infection in the field, only a few percent of the seedlings of progenies of the second back-cross were found resistant. The ‘Antonovka’ progenitors also transmitted mildew resistance, which increased when ‘Lord Lambourne’ was used as a partner, but no immune seedlings occurred in the nursery. With age susceptibility decreased to the extent that a fair proportion of the seedlings were found to be resistant in the field in later years. The degree of scab resistance noted in trees in the orchard was closely relatad to that observed in the greenhouse; orchard and nursery observations significantly correlated for both scab and mildew. There was also a strong correlation between scab infection of the fruits and that of the leaves. Fruit properties of Antonovka offspring of the third generation were on average about the same as those of cultivar progenies.It is pointed out that breeding on the basis of multigenic resistance in large-fruited ‘Antonovka’ selections may not be less efficient than breeding on the basis of monogenic resistance in small-fruited Malus species.

Pre-selection of compact mutants induced by X-ray treatment in apple and pear

SummaryMutation breeding of apple and pear started in 1965 using dormant scions which, after irradiation (X-rays), were grafted on rootstocks. The most efficient dose for apple was around 3 krad, for pear between 4.5 and 7 krad. Primarily shoots exhibiting compact traits were selected, defining such shoots as being thicker than normal for their length or shorter than normal for their diameter while having shorter internodes than normal shoots. The selection was carried out on one-season-old shoots of the same trees during three successive seasons, this involved a cut back at the end of the first and second season. The selected compact shoots yielded with apple on average four times more clones with a distinct compact habit than normal appearing shoots; four out of every five clones were found to be stable in both apple and pear. Averaging the results for apple, 7% of the surviving trees produced shoots the clones of which showed compact growth, this was only 0.5% for pear. In all several dozens of such clones were obtained of the apple varieties Golden Delicious, Coxs Orange Pippin, Belle de Boskoop and Tydemans Early and a few distinct compact and some dwarf clones of Beurré Hardy and Doyenné du Comice.SamenvattingMutatieveredeling bij appel en peer begon in 1965 met enthout dat, na bestraling, op onderstam werd geënt. De doelmatigste dosering lag bij appel om en nabij 3 krad, bij peer tussen 3, 5 en 7 krad, afhankelijk van het ras. De nadruk viel op de selectie van ‘spur’-scheuten cum scheuten met een gedrongen habitus. Zulke scheuten werden gedefiniëerd als scheuten die, afgaande op hun lengte, dikker zijn of, afgaande op hun diameter, korter zijn dan normaal terwijl in beide gevallen de internodiën korter zijn dan bij vergelijkbare normale scheuten.De selectie werd uitgevoerd op éénjarige scheuten van dezelfde geënte bomen gedurende drie achtereenvolgende seizoenen; dit hield in dat na het eerste en het tweede groeiseizoen werd teruggesnoeid. De geselecteerde appelscheuten gaven, na enting, viermaal meer klonen met een uitgesproken gedrongen habitus dan willekeurige normaaluitziende scheuten uit bestraald materiaal. Zowel bij appel als bij peer bleken vier van de vijf klonen ‘stabiel’ te zijn. Bij appel produceerden gemiddeld 7% van de overlevende bomen klonen met een gedrongen groei, bij peer was dit slechts 0.5%.In totaal werden enige dozijnen klonen met gedrongen of zwakkere groei verkregen bij de appelrassen Golden Delicious, Coxs Orange Pippin, Belle de Boskoop en Tydemans Early en slechts enkele bij de pererassen Beurré Hardy en Doyenné du Comice.

Hybrid Tea-rose pollen. II. Inheritance of pollen viability

SummaryPollen viability was evaluated in about 500 seedlings originating from 31 crosses between nine commercial Hybrid Tea-rose varieties. The data indicated that pollen viability was inherited additively.

Pre-determination of survival rate of apple and pear scions after X-ray treatment

SummaryA simple method is described which makes it possible to pre-determine the survival rate of dormant scions of woody crops such as apple and pear after X-ray treatment.During early spring irradiated scions were kept on water in a warm glasshouse and the buds were left to sprout. It appeared that the relation between X-ray dose and percentage of buds surviving on the scions after 3–4 weeks was similar to the relation between dose and the percentage of irradiated grafts surviving after two growing seasons in the field. In sofar the dose at which 50% survival occurs is presumed to be the most efficient one, the method enables speedy determination of the most effective dose of X-ray treatment.